 |
 |
 |
|
Overview
The Oxford Dynamics
plug-in is modeled on the extremely flexible and capable unit used
in the OXF-R3 professional mixing console. Resulting from many years
research into professional dynamics applications, it offers separate
Compress, Limit, Expand, Gate and side chain EQ functions, with full
independent control of all parameters. Features such as selectable
time constant curves and variable soft compress functions allow the
user to confidently tackle all common uses of compression, from subtle
unobtrusive level control and mastering functions to the production
of great artistic effects. The use of a feed-forward architecture with
logarithmic side chain processing, making use of look-ahead techniques,
ensures exemplary sonic characteristics and dynamic accuracy, with
an artistic capability simply unavailable from other single units,
analogue or digital. This highly sophisticated and professional product
has the power and flexibility to obviate the need for many of the separate
applications most users keep for specific uses.
Features
Channel Dynamics with separately controlled sections for Compressor, Limiter, Gate and Expander.
Channel Dynamics includes fully featured 2 Band side chain EQ which can also be used in signal path.
Separate Bus Compressor / Limiter with surround multi-format support
and selectable Sub channel filtering and gain contribution control. Selectable linear and exponential time constant curves.
Highly accurate logarithmic side chain processing.
Fully variable soft ratio function for extreme programme tolerance and highly musical compression.
Variable harmonic enhancement for extra loudness, presence and 'punch'.
Selectable re-dithering function for word length reduction in mastering situations.
Extremely low signal path noise and distortion, below -130dBr.
All functions are fully automated.
Platforms Supported
Pro Tools HD (TDM), Pro Tools LE (RTAS), M-Powered (RTAS), PowerCore, AU, VST
General The Sony Oxford Dynamics plug-in is a highly
sophisticated device with comprehensive control of many parameters.
Therefore, to aid operation, there is separate page of controls for
each process, since it would not be feasible to have all controls and
displays available on a single page.
Although there are four gain level controlling processes, Gate,
Expander, Compressor and Limiter in the mono and stereo plug-ins, their
control signals are all derived from a single side-chain detector,
operating on a single gain control element. The amount of processing
necessary to allow a detector for each process would be far too great
for current processor capabilities, if done correctly.
The 5.1 Buss Compressor does not include gating and and expansion, but as an additionally has a Sub Filter section.
Feed-Forward Architecture
The type of architecture in the Oxford Dynamics uses feed-forward
techniques. In this case, a tiny delay is introduced into the signal
path. (The amount of delay is virtually insignificant, and can be
compensated for, in order that all signal paths are aligned, in any
case.) This delay allows time for the side-chain control signal to be
generated so that it can coincide exactly with the signal it will
control. This technique allows very accurate control of the audio
levels by generating totally precise control signals, thus preserving
audio quality. Gate The gate acts like a switch, where signals below
the THRESHOLD setting are attenuated, according the the RANGE control
setting. This type of function is useful for suppressing unwanted
background noises, such as tape hiss, where the wanted signal is well
defined. Gates are very useful on drums and percussive instruments too.
Once the signal reaches levels above the THRESHOLD, the gate opens
allowing the signal through at full level. When the signal level falls,
it must reduce to 4dB below the THRESHOLD before the gate will close
again. This is known as 4dB of hysteresis. Increasing the ATTACK time,
softens the attack 'edge', and the RELEASE sets the time for the
closure take to take place. The HOLD sets the minimum time before the
gate is able to close again. Expander
The expander has all the same controls as the gate with the addition of
a RATIO control. But whereas the gate acts like a switch, allowing the
full signal through once the THRESHOLD has been reached, the expander
allows the signal level to increase, according to the slope of RATIO
setting. This function can be used to lower background background
noises but is particularly useful for increasing the dynamic attack of
any musical instruments which are percussive nature, such as drums,
percussion and acoustic guitar.
Compressor
The compressor allows gain reduction to signals beyond the level set by
the THRESHOLD according to the RATIO setting. The RATIO can be set
anywhere between 1:1, where no compression takes place, and 1000:1
where virtually total limiting takes place, meaning that there is no
increase in level whatsoever for signal level beyond the THRESHOLD.
The ATTACK determines how quickly the compression sets in, allowing
initial transients to pass, with the longer settings, useful to pass
the intial attach of percussive intruments. The RELEASE sets the time
taken to recover to no gain reduction, once the signal has returned to
a level below the THRESHOLD. The start of the RELEASE phase can be
further delayed by increasing the HOLD control.
The transfer curve of the compressor will normally show
a corner at the THRESHOLD point, the transition between no gain
reduction and gain reduction. This corner can be 'smoothed' using the
SOFT function which helps to 'hide' compression.
When compression takes place, the overall signal is
reduced at the higher levels, normally requiring the level to be 'made
up' again. The MAKE-UP gain control allows for this. Limiter
The limiter is designed to set a fixed ceiling for signals according to
the THRESHOLD setting. Although it does have an ATTACK control which
can allow initial transients to pass, at the medium and fastest ATTACK
setting, the signal can be retained so as not to exceed the THRESHOLD.
This is achieved with 'feed forward - look ahead' techniques and allows
initial attack transients to be significantly modified without
breaching the THRESHOLD setting. Limiters were originally designed to prevent transmission
systems being overloaded but are often used as artistic tools too. The
ATTACK, HOLD and RELEASE behave in a similar manner to those of the
compressor, but have different ranges. Side-Chain EQ
The side-chain equaliser is a fully parametric 2 band section. Its main
purpose is to allow modification of the frequency response of the
side-chain signal path for functions such as 'de-essing'. It is
possible to use it in the main signal path alone as an additional 2
band equaliser, or it can be used in the side-chain alone, or for both
the signal path and side-chain combined. Warmth
The AMOUNT control allows the addition of harmonically related signal
with a tube or electronic valve like characteristics. Signal increases
of up to 6dB can be achieved within the audio, but without going over
the digital maximum. MAX TRIM allows fine tuning in order to compensate
the peak level. The warmth function is indepedent without dependency on
other dynamic processes. Buss Compressor (Pro Tools HD & PowerCore only)
The buss compressor plug-in includes a 5.1 wide compressor and limiter
where the sub channel has some additional individual control.
The 5.1 compressor, limiter and warmth sections have exactly the same
controls and parameters as the mono and stereo. Additionally for the
sub channel, the LP FILTER sets the cut off frequency, the SUB TRIM
sets the contribution of the sub signal to the side-chain, and the SUB
PASS sets the amount of gain reduction control passed to the sub
channel.
System Requirements
Pro Tools
Pro Tools 6.0 or above
Approved Pro Tools CPU, OS and hardware configuration. More details: www.digidesign.com
Mac OSX 10.3 or later
(Leopard supported see Digidesign for details)
Windows XP
/ Vista32RAM 1GB minimum
iLok key with latest drivers
Audio Units
Audio Units compatible application (Logic, Digital Performer etc.)
Mac OSX 10.4 or later
(including Leopard)
RAM 1GB minimum
iLok key with latest drivers
VST
VST compatible application (Cubase, Nuendo, Acid etc.)
Mac OSX 10.4 or later
(including Leopard)
Windows XP
/ Vista32
RAM 1GB minimum
iLok key with latest drivers
PowerCore
TC PowerCore hardware
PowerCore version 3 drivers
AU or VST host application
Mac OSX 10.4 or later (including Leopard)
Windows XP / Vista32
RAM 1GB minimum
iLok key with latest drivers |
|
Dynamics Function
The Dynamics section comprises of four separate applications,
Compressor, Limiter, Gate and Expander. Although these applications
contain several control types that have common functions, the
operation, ranges and laws of these controls have been optimised
carefully for maximum flexibility within the intended specific use of
that section. The very wide control ranges offered within the
applications are accommodated in the GUI using specific control laws
that encourage experimentation over a very wide parameter set without
the loss of finer control sensitivity and detail. Careful consideration
has also been given to the dynamic behaviour of the time constants, as
this factor is largely responsible for the sonic character of the
dynamics application. In order to make best use of this application it
is necessary to gain a basic understanding for dynamics processing in
general and the particular architecture of the Sonnox Oxford Dynamics
plug-in. The following sections address these issues. Basic Compressor Architectures
There are two basic types of dynamics architecture in common use; these are often
termed as feed-forward and feedback types. The feedback type uses it's own output
to compute required gain reduction. This method had an advantage in early analogue
compressors because the complex and largely unpredictable laws of early gain
reduction elements could be somewhat decoupled from the total level transfer
characteristic of the application (because the design made use of level feedback).
With the introduction of better solid state VCA's and accurate logarithmic side
chain processes, this method has largely been abandoned in favour of the feed
forward model since it has a much greater degree of control parameter separation
and intrinsic accuracy.
Feedback Model
The Sonnox Oxford Dynamics section is a feed forward type processor. By
that we mean that the gain controlling side chain element of the
processor works by evaluating the programme level at the input,
calculating the required output gain by dead reckoning. This widely
conforms to the architectures of most popular modern analogue dynamics
sections employing voltage-controlled amplifiers. In a digital design
the feed-forward model has additional advantages, which include the
possibility of extremely well controlled and variable time constant
laws and sonically accurate gain control elements. Also look-ahead
processing (using delay) allows gain control to be initiated in advance
of the signal without signal quality loss.
Feed-Forward Model
Compressor Level Control Functions
There are two main factors that describe compression function; level
versus gain function, which is generally assumed to be independent of
the time constants, and dynamic gain function which exhibits more
complex dynamic behaviour over time. In explaining the operation of the
compressor section, it is useful to split these categories. The
following section refers to the level versus gain behaviour of the
compressor application of the Sonnox Oxford Plug-in.
The Sonnox Oxford plug-in employs logarithmic side
chain processing, which means that all signal parameter setting (and
time constant action) occurs in the ‘decibel' domain. This makes it
possible for all control functions to remain independent and therefore
provides the greatest level of control for the user. To get the best
results from the application it is useful to gain an understanding for
the specific effects of the control parameters.
Compressor Threshold Control
The threshold control sets the level (ref dBFS) that compression and
gain reduction will begin. The control has a linear decibel law over
the range. The following is an illustration of the threshold control
operated at 5dB increments with the ratio at max (1000:1) to –20dBr.
Compressor Ratio Control
The ratio control sets the rate at which gain reduction will occur when
input level goes beyond the set threshold level. The control has a
1/Ratio law so that gentle compression can be achieved despite the wide
range of the control. I.e. from 1:1 to 2:1 ratio occurs over the first
50% of the control range and 4:1 ratio occurs at 75% control rotation
etc. Full limiting is achieved at 100% control rotation.
Compressor Soft Ratio Control
The soft ratio function provides a gentle, minimum rate transition
between the region below the threshold and the compressed region of the
curve. A further threshold below the main threshold control setting,
defines the start of the soft curve. The program signal is therefore
compressed progressively harder as it gets louder within this region
until the full compression defined by the ratio control is achieved.
The adjustment range via the Soft button is from 0dBr to –20dBr in 5dB
increments.
Compressor Gain Control
The gain control allows manual compensation for level loss during
compression to a maximum of +24dBr. This control operates independently
from all other settings and can be considered as an output level
control. The gain control is applied to all Dynamics functions but
operates only when the compressor in ‘IN'.
Using Level Control Functions
Since all level control functions in the Sonnox Oxford Dynamics
Compressor operate entirely separately, a very high degree of control
for a wide range of common use is possible, in particular the plug-in
does not impose any particular style constraint on the user. The
section explains some of the commonly used techniques and how they can
be achieved using the Dynamics plug-in.
In the most general terms the extremes of compression usage falls into
two main categories, dynamic level control and sound effect generation.
For simple level control, such as controlling performance variation in
vocals, instruments and final programme, we most often require the most
transparent compression with minimum artefacts due to the dynamic
control. However, to generate sound effects and distortion the reverse
is true and we need to make the sound character of the compression a
dominant part of the final result.
In order to understand how we achieve these two different styles of
result we must remember that in general we are much more sensitive to
the rate of change of level than we are relative gain. So in order to
generate prominent sound effects from the compressor we need to
generate significant rate of change of gain action by using both hard
compression gain curves and the creative use of time constants. However
for general unobtrusive level control we should be avoiding all of this
and opting for the gentlest compression gain curves and least obtrusive
time constant settings that integrate well with the programme style.
General Programme Compression
There are 2 main basic philosophies that underlie approaches to
unobtrusive compression. This section aims to explain these concepts,
make comparisons between them and show how enhanced results can be
achieved using the Sonnox Oxford Dynamics plug-in compressor.
‘Least Possible' Approach
The first and most obvious, which I will call the ‘ least possible
approach' is to leave the majority of the programme uncompressed,
forcing the compression to deal only with the louder passages. This
method has a definite psychological advantage in that one gets the
feeling that the majority of the programme remains unaffected. There is
also some possible technical merit (especially for legacy designs) in
that the compressor is working ‘less often' and over a restricted
range, thereby avoiding some of the potential errors in the
application.
The above plot illustrates this kind of approach. The idea is that the
programme goes ‘over' on the loud passages so we seek to control the
loud portion only by setting the threshold relatively high (-5dBr) and
setting the ratio high enough (i.e. between 3:1 & 4:1) to prevent
the over. With the Sonnox Oxford compressor the threshold and gain make
up controls can be used to accommodate this approach over a 24dB range
of relative input levels without change in the sonic character of the
programme.
This method has the major disadvantage of risking increased rate of
change disturbance because the transition between non-compressed and
compressed programme regions is sharp. Therefore there is a
considerable reliance on longer time constant settings in order to
reduce the sonic effects of the compression. I.e. we need to seek to
control the rate of change using time slewing rather than level
progression. Whilst this approach would naturally form a good basis for
using the compressor as a sound effect, it is less suitable for
composite programme control.
One way to alleviate the compression transition effect is to smooth it out using the soft ratio function.
The above plot shows the action of soft ratio set to 5dB applied to the
previous settings. Starting the compression earlier and increasing the
compression ratio up to the max level point smoothes out the transition
point at the onset of compression. The main advantage of this method
(often referred to as ‘over easy') is that faster time constants can be
used before the compression artefacts become too obtrusive. This means
that the programme can be made to sound louder and more present without
increasing peak levels, despite the fact that more of it is being
compressed. Also, the use of faster time constants further reduces peak
overshoot, so there is less need to employ limiting to the signal
chain.
It should be noted that with the Sonnox Oxford plug-in, the application
of the soft function will always result in the same maximum level
output. This means that you can apply the soft ratio function at will,
with only a minimal need to adjust the threshold and ratio controls.
Combined Approach This concept advocates that a more transparent
sounding compression can be achieved if a relatively large portion of
the programme level range is under continuous compression. The
rationale here is that the rate of change disturbances are minimised
because the compressor spends less time going over the onset of
compression transition range. But the downside is that peak loudness is
less well controlled, therefore quite heavy additional peak limiting is
sometimes required to tailor the performance into an overall mix. 
Maximum Loudness
Minimum Obtrusion
This plot shows a minimum intrusion type curve using a ratio of around
2:1 and a soft setting of 10dB. This style of compression will bring up
the softer passages by around 12dB and progressively compress the loud
passages into half the original dynamic range in a very subtle and
unobtrusive fashion. Settings of this kind can tolerate fast time
constant settings without obvious sonic artefact and are therefore very
effective in classical music programme or other situations where a good
degree of dynamic realism needs to be preserved. Back to Top
Timing Functions
The relationship between gain compression and temporal behaviour is
absolutely crucial to successful dynamic control, whether the user is
aiming for unobtrusive control of levels or a completely stylised sound
effect. Much of the artistic characters of the massive range of
renowned compressors are determined by subtleties in the timing
behaviour of these units under complex musical signal conditions.
In order to encompass as much of this valuable artistic legacy as
possible, the Sonnox Oxford compressor plug-in incorporates a very wide
range of timing control, using both linear dB and exponential dB time
dependency curves. In this way the plug-in can be used to create the
widest range of artistic effect without imposing an overwhelming and
unavoidable character of it's own. The plug-in should therefore be
considered as a powerful and flexible tool rather than a specific
‘style' of compressor. The following section describes the operation of
the compressor timing controls and time dependency behaviour.
To generate the timing illustration plots the following stimulus was
used for reference. This is a tone burst signal that consists of 0.2S
of full level signal preceded and followed by 0.8S of signal at –20dBr.
Compressor Attack Control
The attack control varies the timing behaviour of the compressor at the
onset of gain reduction, either due to the arrival of a peak level
above the threshold or the further increase in a level already above
the threshold.
The three plots above show the action of the attack control from minimum through mid range to maximum setting.
Compressor Release Control
The release control varies the timing behaviour of the compressor
during the recovery period after a gain reduction, when the signal
level has reduced from previous levels above the threshold.
The above plots show that action of the release control from minimum to
half range (maximum range is too long to show successfully on this
plot). Compressor Hold Control The hold control varies the
amount of time between a reduction of levels above the threshold and
the onset of the release time. It provides a period after gain
reduction where a slower rate of recovery occurs.
The above three plots show the action of the hold control from nearly
minimum to 75% of maximum with an intermediate position with the
release set to minimum. When the compressor is in recovery after a loud
passage, the full value of the release setting time is reached only
gradually over the period of the hold time. This produces and extended
period when the release time is maintained at slower rates in order to
allow faster gain recovery without excessive distortion at low signal
frequencies. Since the release time is effectively multiplied by the
hold time, very long total gain recovery times can also be obtained by
using the release control in conjunction with the hold control. Compressor Timing Laws The Sonnox Oxford compressor offers
three compression types called Normal , Classic and Linear. The time
constant laws employed define the major difference between these types.
The Sonnox Oxford Dynamics uses both exponential dB/time and linear dB/time laws as illustrated below.
Exponential d/B curve used in Normal & Classic type
Linear dB curve
The Sonnox Oxford dynamics time settings are displayed as real time
constants when in exponential mode. In linear mode the display is
scaled to correspond to the time required for a 10dB change of level.
This provides a degree of parity between the perceived timings of the
two laws, which facilitates comparison and selection between
compression types. These two laws have very different sonic
characteristics. Exponential dB Timing (Normal & Classic types) The
exponential/dB curve is by far the most popular law used in a great
many well-respected compressors and is the natural result of more
recent analogue units employing logarithmic side chains and
resistor/capacitor time constants. The exponential/dB law has some
interesting characteristics. Firstly, the time taken to complete a
compression event tends to stay the same however large the dynamic
signal excursion is. Also since the peak rate of change of gain
increases with dynamic excursion, the resulting harmonic content due to
compression tends to follow the loudness of the programme in a way the
ear expects. This helps to mask the effects of the compression and thus
provides the most forgiving solution, being tolerant to differing
timing settings and programme material. This makes it the best choice
for general compression use and overall dynamic control of complex
musical programme.
The plots above illustrate the action of the exponential law, the first
shows 10dB gain reduction (scaled for comparison) and the second one
shows 30dB. As can be seen, the initial rate of change is much
increased in the attack period and the total time for attack is similar
despite the increased level transition.
The Classic type selection is a subset of the Normal type with timing
controls fixed to nominal values to match a range of popular legacy
units. All other controls behave as the Normal type. This type
selection is quick to set up and is most useful as a general-purpose
channel compressor. Linear/dB Timing (Linear type) The linear /dB law in some
respects has the reverse behaviour of the exponential law. Because the
rate of change of gain is constant (as set by the timing controls), the
greater the signal dynamic excursion the longer the compressor will
take to complete a gain change. Also, since the total time that the
compressor spends in attack or decay is proportional to the size of the
gain excursion, the harmonic content of the compression artefacts will
seem to reduce in frequency content the louder the signal excursion is.
This type of compressor is useful for generating dynamic sound effects
because the sonic character of the compression is much more affected by
time control settings and programme material than the exponential type.
The above plots illustrate the action of the linear law. The first
shows 10dB gain reduction (scaled for comparison) and the second one
shows 30dB. The rate of change is the same during the attack period and
therefore the total time for attack (and subsequent release) is
increased with greater level transition.
Please
note that the linear timing law is generally unsuitable for the control
of programme dynamics and modulation levels because of its unnatural
sounding relationship between level excursions and perceived overtone
generation.
Using Compression Timing Functions The
setting of timing functions can drastically affect the sonic character
of compression and there are many different approaches to compression
timing, often in pursuit of ever-changing fashion. Therefore there is
no right or wrong approach to this task. However to successfully build
up your own portfolio of artistic sounds using a variable parameter
compressor such as the Sonnox Oxford plug-in a basic grounding in the
sonic effects produced by timing is useful. The following section sets
out to describe the basics of timing settings and the range of sonic
effects available from the Sonnox Oxford plug-in. By changing time
constants many effects can be generated such as:
Attack times can accentuate and bring percussion instruments forwards if slow and push them into the background if fast.
Attack times can re-model the sound of a percussion instrument by creating
gain overshoots if relatively slow, i.e. make a soft event produce a harder
sound, or fast attack can soften a hard sound by attenuating it's peaks.
Fast
attack with fast release can generate pleasing harmonic distortion and
‘warmth' that is focussed on the lower frequencies of a sound by
modulating the gain during the period of the musical waveform.
Fast
releases can significantly increase the relative loudness of programme
by filling in the programme with accentuated ‘quiet passages'. A slow
release will do the opposite.
Moderate to fast release times can lengthen apparent reverb time.
Moderate release times can accentuate the musical timing of piece if set to recover during the natural rhythm of the music.
There are many approaches to programme level control, which are largely
decided by whether one is trying to get maximum loudness and
excitement, enhancing reproducibility at low reproduction levels or
just trying to control overloads. In mastering situations either or all
of these may be appropriate along with many other subtleties such as
matching impressions between tracks destined for an album release. The
following is a general description of the some effective approaches and
starting points. Fast as Possible Approach To obtain absolute maximum
modulation and minimum dynamic range the best approach is to set
release times to minimum, increase the hold time just enough to the
reduce LF distortion to acceptable levels and increase the attack time
just enough to allow some overshoot on percussive peaks, in order to
retain some impression of programme dynamics. The appropriate level of
compression can then be obtained using the threshold, ratio and soft
ratio controls. The overshoots produced by the attack times can be
controlled by the use of the programme limiter section. Natural Dynamics Approach
To obtain a more natural compression a good starting point is to set the
attack and release controls to mid positions with hold control at minimum
(this is the fixed setting of the Classic compressor style). This approach
aims to match to some degree the dynamics of the ear's response and recovery
from loud sounds at relatively high sound pressure levels. Variations on
these moderate settings can yield realistic results if appropriately adjusted
to suit the intended reproduction levels of the programme.
Slow and Gentle Approach
For level control with the least possible intrusion the method is to set
the attack and release times to the longest possible times, perhaps with
the addition of the hold control to increase the release times further.
This ensures that the highest levels within the programme are controlled
gently and the gain recovery in the quiet passages is almost imperceptibly
slow. This method is most effective when used in conjunction with the larger
soft ratio settings, as this ensures that compression commences well before
the target maximum level, providing a degree of prediction.
Artistic Effects
The manipulation of timing within compression can create some very useful
sound effects. In particular gain overshoots produced by slow to moderate
attack times can be very useful at tightening up soft percussion sounds.
However a note of caution is needed for users of workstation applications
in that effects such as these may cause unexpected programme clipping that
may prevent the available range of possible sounds being fully appreciated.
In particular, for systems that lack overload margin between plug-ins or
within their mixing structures, the extra short term peaks produced by creative
compression may be prematurely clipped within the host application because
essentially there is no range (headroom) to accommodate them. In this case
a reduction of input levels and/or a suitable reduction of the threshold
and gain make-up values may be needed to fully realise the new sound within
the intended mix.
Limiter Functions
From a level profile perspective the limiter function is essentially the
same as a compressor set at infinite ratio. However the use of much faster
attack times with a somewhat different dynamic behaviour allows faster and
more effective reduction of peak levels. Historically limiters were developed
mainly for radio transmission systems where absolute limits on modulation
were needed.
In this case simple saturation was not useful since the HF energy produced
by signal clipping could still breach modulation limits. The earliest
limiter designs were mostly fast attack slow release types to minimise
audibility problems. Since then many different designs and much more complex
methods have been developed. And more recently limiting and its side effects
has almost become an artistic tool in itself, being partly responsible
for the recent trends for absolute maximum modulation and loudness, currently
favoured amongst producers and broadcasters of popular music. As a result
of this expanding trend for stylised dynamic control, the demarcation
between limiting, compression and even EQ has become increasingly blurred
as an increasing number of ever more complex devices become available
that make use of all of these functions in a quest to produce impressive
results.
The Sonnox Oxford plug-in limiter however is presented as an entirely separate
and direct process that is designed and optimised specifically for highly
efficient and musical peak limiting functionality. Despite being simple
and intuitive to understand and operate, superior results are obtained
from highly accurate level and timing behaviour making optimal use of
look ahead processing that acts on signal peaks prior to their arrival
at the gain control element. Although the limiter is designed to complement
the compression section of the Plug-in, it can be equally well be used
as a stand alone application for enhanced peak level control and programme
modulation maximisation etc.
General Description
The limiter function
controls are presented similarly to the compression function except that
there is no ratio control. The time constant functions, although similar
to the compressor, have different ranges. In particular the attack time
can be adjusted to be much faster than the compressor. It should also
be noted that the threshold levels are related to the output level of
the whole dynamics application (rather than the input level), such that
any gain increases produced in the compression section and gain make-up
do not affect the calibration of the limiting target levels.
General Limiter Operations
There are many methods and approaches to programme limiting that are
favoured amongst users. In general however these fall into two main
categories as described below.
The least intrusive kind of limiting is achieved with a fast attack and
a relatively slow release, adjusted to suit the general timing of the
music. Very long decays, often favoured in classical music productions,
can be achieved with the Sonnox Oxford limiter by using a combination
of both release and hold times. Due to the look ahead processing, the
Sonnox Oxford limiter also has a significant range of attack time that
can be used without peak level overshoot. This means that a slower and
gentler limiting can be achieved during the onset of loud passages
within the programme material without breaching maximum levels as set
by the threshold control. Maximising the Loudness Using the Limiter
A recent popular use of programme limiting aims to maximise the relative
loudness and average modulation of the music by reducing the short-term
peak levels within the programme waveform. This makes it possible to increase
the overall volume (gain) of the piece without getting obvious overloads
(red lights) on the final mastered work. The success of this method depends
on the amount of peak reduction can be obtained without objectionable loss
of quality to the programme. Maintaining the quality of the peaks without
reproducing their maximum levels relies on a degree of ‘peak remodelling'.
The basic approach to this function is to initially set attack, hold
and release controls to minimum for fastest possible action. Then
reduce the threshold control to progressively reduce the gain of the
programme, only during the very short periods where peaks occur. The
sound of the peaks can then be adjusted by increasing the attack period
to soften the edges such that a degree of realism is retained despite
the reduction of instantaneous levels during that period. Since the
Sonnox Oxford limiter has a fairly large look-ahead period, it is
possible to increase the attack time significantly without allowing the
peak levels to pass. It is therefore possible to re-model the limited
peaks considerably in real time, retaining good programme realism
despite large degrees of peak reduction. If it is necessary to increase
recovery times after peaks, for instance due to LF modulation content,
it is better to use the Hold control for this purpose, as the recovery
time is faster for a given overall period than by increasing the
release time. The programme level can then be increased so that the new
peaks just reach maximum level again. Depending on the material,
average programme modulation may be increased by 6dBr or more by this
method.
Expander Functions
The Dynamics expander section control functions are presented similarly
to the Compressor and Limiter sections, except that a Range control is
added. The architecture of the expander conforms to what is often
described as ‘downward expansion', which means that the application
only works to attenuate existing signals below a set threshold and
cannot produce any additional gain for signals above the set threshold
levels. In practice this means that, although the purpose of the
expander is to increase dynamic range, it can only achieve this by
reducing the signal level in the first place. The Threshold control
sets the level beneath which the expander will become active.
The Ratio control sets the gain slope rate that signals below the
threshold will be attenuated with respect to the input levels.
The Range control sets the bottom limit that any attenuation caused by expansion can reach.
Expanders are used for many purposes, both technically and
artistically. These include background noise reduction and file clean
up, ambient noise disturbance reduction in live recordings, presence
and dynamic profiling of instruments and creative control of ambient
reverb etc. Because the Sonnox Oxford expander has 20 samples of signal
pre-view, it is particularly useful for instrument dynamic profiling as
it can act on the signal before gain control actually occurs, meaning
that one can actually profile the leading edge of a percussive attack
for instance.
Gate Functions
The gate section controls of the plug-in are presented in the same way
as the expander function except that there is no ratio control.
Programme gating has become ever more popular in recent years since its
inclusion in some professional console systems. Originally intended as
a technical tool for tape noise suppression and such, many useful and
often fashion changing artistic effects have been achieved using gates.
The Sonnox Oxford plug-in gate has many advanced design subtleties that
are based on long experience in the artistic use of gating.
The basic architecture of a gate is similar to expansion with infinite
ratio and therefore acts much like a programme switch. Signals below
the set threshold are cut and only those above this are passed to the
output. The gate also has level hysteresis such that once opened by
signal above the threshold, a subsequent signal level reduction of 4dBr
is required to close it again.
The residual signal level for programme below the threshold is set using the Range control, as in the expander section. Since the gate effectively operates on signals before gain control is affected, the Attack
control can provide a significant range of attack profiling without
missing the peaks within the programme. This provides the capability to
change the sonic character of the attack period of the gate.
The Hold
function provides time hysteresis by effectively providing a delay
after gate opening before subsequent closure can occur, which is very
useful for trimming gate activity to match programme event timing
durations and nested rhythms within the music.
The Release control provides the ability to tailor the recovery period to match the programme material and provide artistic effects.
Side Chain EQ Functions
A high specification two-band side chain EQ is provided to allow
de-essing and other modifications of side chain frequency response. The
EQ processing section may be routed to either the dynamics side chain
or the main signal path or both simultaneously, via independent EQ-Side
chain and EQ-Signal selector buttons.
Harmonic Generation
Although there is much discussion of the importance of level and time
responses in defining the character of dynamics and compression
applications, these are not the only parameters that affect the user's
experience of these applications. As stated within the previous texts,
many original and much loved legacy units have gained their reputations
for sound quality based on inherent characteristics produced as
by-products of their signal chain and gain control regimes. Indeed some
tube-based units are favoured as much for their basic sonic character
when inserted in the signal path, as for their programme compression
characteristics. This is almost invariably due to accumulated signal
path distortion and novel overload characteristics when in static mode,
or a more complex combinational modification of these effects during
dynamic gain control conditions.
In recognition of the important artistic dimension that these effects
confer to the dynamics process, the Sonnox Oxford Dynamics plug-in
includes processing functionality destined to endow an appropriate
harmonic character to the dynamics function, in a similar vein to those
often experienced when using legacy units of renown. However due to the
controllability and accuracy of the digital signal path, this character
can be controlled by the user, rather than simply being an inherent and
unavoidable side effect of the application. Warmth Function
This process confers additional
loudness, punch and definition to the sound of the dynamics section.
The operation of this process is to impose a harmonic profile onto the
signal that increases the density of higher value samples within the
programme, in order to boost average modulation levels without an
increase in peak levels or the risk of digital clipping. The warmth
function is engineered to achieve this without loss of dynamic
information within the programme.
Another very
important purpose of the Warmth function is to accommodate internally
generated levels up to 6dB greater than notional digital maximum
without causing increased peak levels or hard clipping. The main
advantage is that short term level peaks and overshoots, resulting
naturally from the artistic use of compression, can still provide
harmonic information to the programme even though they may represent
levels above maximum digital modulation, that would be subjected to
hard clipping if left untreated.
The process also adds subtle warmth to the programme material that is
reminiscent of tube systems and is similarly tolerant of overloaded or
previously clipped signals, avoiding much of the harshness associated
with these conditions. Significant artistic effects may therefore be
achieved by deliberately overdriving the warmth processing by
increasing the compressor gain make up beyond normal levels and
allowing the warmth processing to control the peak signal levels.
When selected, the Warmth function operates on the complete signal
chain of the dynamics plug-in and is therefore applied to the signal
even if no compression functions are operative.
|
|
|
 |
|
 |
|
|
|
