Signal Flow
The following diagram illustrates the overall signal flow within the Oxford Reverb application:Controls Layout
The control functions are arranged in operational sections, comprising of early reflection settings, reverb tail settings and contribution mixing functions. Mixing functions are conveniently split into separate sections, for internal signal contribution to the reverb tail section and overall level control and mixing functions.Input
INPUT GAIN fader controls the overall input level and reverb gain.INPUT METER displays the peak input level to the reverb processing after the INPUT GAIN fader.
STEREO SEPARATION fader controls the degree of left and right signal mixing at the input of the entire reverberation processing. At minimum setting the internal input to the reverb is equivalent to a mono mix.
LF ROLL-OFF fader provides the means to reduce the level of LF programme entering the reverb processing. The control is continuously variable from minimum position where no LF roll-off occurs to maximum LF cut at highest setting. The response of the input signal at the Wet/Dry mix stage is unaffected.
Early Reflections
Note: Early Reflections are often referred to as ER.SHAPE buttons select the overall shape of the early reflection space. Four basic space shapes are provided to allow the application of appropriate overall character to the reverberation.
POSITION fader controls the relative back to front placement of the listening position within the virtual room simulation.
SIZE fader sets the overall size of the simulated space, as measured between front and back walls. Room shapes remain in proportion with this size.
WIDTH fader c ontrols the stereo separation of the room reflections depending on their particular direction within the stereo field. Normal position placement occurs with the control at minimum setting. Increasing the setting provides wider separation. Increasing settings beyond 100% produces ultra-wide separation, often useful when adding spatial effects to single mono tracks.
TAPER fader controls the loudness level of the reflections depending on their relative path lengths. I.e. longer delays are progressively reduced in level because the sound will have travelled further. Increasing the taper control will proportionally increase the relative contribution from long path lengths in relation to short paths. At maximum setting all paths lengths will have equal level contribution.
FEED ALONG fader controls the amount of re-injection of distributed sound within the simulated space. Greater re-injection will result in greater reflection density and echo complexity and cause the reflections to continue over a longer period of time.
FEEDBACK fader controls the proportion of the reflected signal that is re-circulated within the room simulation. Increasing feedback will result in longer reflection duration (room reverb time) and greater room mode frequency response effects (boominess).
PHASE SELECT button modifies the phase relationship of the Feedback variable. Modified phase (preferred on position) will result in softer reflections over time and produce greater modal and spatial dispersion, synonymous with natural rooms containing objects that disperse reflections and tend to break up room behaviour. Normal phase (off position) will result in harder reflections and greater modal frequency behaviour.
ABSORPTION fader controls the high frequency roll-off that naturally occurs over time due to absorption. Higher settings (greater absorption) relate to spaces containing soft furnishings and wall coverings, low settings (less absorption) relate to empty spaces with hard reflective surfaces etc.
Tail Mix
Facility is provided to drive the input of the reverb tail processor with a combination of signals comprising of; untreated input signal, delay compensated input signal and the output of the early reflections processing. Two levels of cross fade control are provided for this mixing function, so that relative contributions can be varied freely without disturbing overall levels.COMP DELAY fader s ets the timing of the delay compensated input contribution to the reverb tail processing.
With the ER TRACK button selected the delay compensated input signal tracks the notional size of the early reflection processing section. The available control is from zero to 2 times the early reflection Size setting, with mid position (1) representing the normalised time alignment setting.
With ER TRACK unselected, theCOMP DELAY control is uncoupled from the early reflection Size setting and provides an independent delay up to a maximum of 30 meters.
ER MIX fader provides a cross fade between the untreated input signal and the output of the early reflections processor. TAIL INPUT fader provides a cross fade between a delay compensated versions of the input signal provided by the COMP DELAY fader and the mixed signal resulting from the ER MIX stage.
Please note that a combination of the input signal and delayed signal together can cause unwanted frequency combing effects when the ER SIZE is set for smaller spaces. It is therefore best to arrange the ER MIX and TAIL INPUT controls to predominately use either a mix of the ER and the input, or the ER and the delayed input when simulating smaller spaces.
Reverb Tail
All parameters of the reverb tail section are fully compensated, so that they may be adjusted in isolation without mutual interaction with other control settings. This means that settings such as REVERB TIME or LF ROLL-OFF will produce constant results even if other factors such as DISPERSION or OVERALL SIZE are varied.REVERB TIME fader sets the overall reverberation time in seconds as referred to a decay of –60dB ref the input stimulus.
OVERALL SIZE fader sets the overall size of the delays within the reverb tail section, providing the means to modify the character of the reverb independently of reverb time and absorption parameters. Larger size settings generally provide the greatest impression of space but result in slower density build up in the short term. Shorter size settings produce faster density build up over time, but exhibit greater tonal artefacts in the longer term.
DISPERSION fader controls the rate and character of the build up of dispersion behaviour, complexity and sonic texture over time. At mid position (0) no extra dispersion is added. Positive values cause increasing dispersion and complexity over time. Negative values also cause increasing dispersion but it is modified to produce greater differential dispersion between left and right signals.
PHASE DIFF fader operates in conjunction with the DISPERSION, setting to control the build up of phase difference between left and right stereo signals. The greater the setting, the faster phase differences will build up over time, and cause a widening and deepening of the stereo sound field.
Positive values will create a build up of left and right difference, which is largely limited within the same absolute polarity across the sound field as the original programme signal. This is most useful for producing a natural reverb sound fields that spread between the confines of the stereo speaker width.
Negative values produce a wider range of phase dispersion that includes components that have inverse polarity with respect to input programme and left and right outputs. This is useful for producing sound fields that seem to extend beyond the stereo speakers to produce an enhanced sense of immersion within the simulated space.
PHASE MOD fader controls the application of internal phase modulation to the reverb algorithm. This adds a very slight variance to the reverb character over time, which enhances realism and presence under many conditions.
ABSORPTION fader controls the high frequency absorption effect within the reverb section. Higher value settings produce greater overall HF roll-off and faster relative absorption over time, synonymous with natural spaces containing a variety of absorption materials such as wall coverings, curtains or furnishings etc. DIVERSITY fader provides statistical front centre weighting to the reverb tail, which is often required to anchor the reverb effect to centre stage of stereo sound field mixes. Centre weighting is greatest with the diversity control in minimum position where the reverb image will seem narrowest. In maximum position no centre weighting occurs and the reverb image is therefore equally spread across the sound stage, producing the greatest spatial diversity and the widest perceived image.
Output
REVERB MIX fader provides a cross fade between the early reflections and reverb tail for the final output.WET/DRY fader provides a cross fade between the input signal and the output of the whole reverberation processing.
100% WET button forces the output to reverb only. This is convenient when used in mixing applications where the reverb commonly forms part of an auxiliary mix where the dry signal is present on the main mix buss.
OUTPUT METER displays the peak output level from the reverb plug-in.
Reverb Equalisation
The Equalisation section comprises of 5 bands with the upper and lower sections selectable between band pass, shelving and 12dB/octave filtering functions. The EQ processing proceeds the reverb processing and therefore the dry signal remains unaffected by Equalisation settings.IN buttons t oggle the EQ of the associated section in and out for comparison purposes.
GAIN knobs Control the effective gain of the EQ curve from –20dB to +20dB. The default curves for all EQ sections are band pass or 'bell' shaped, where boost and cut curves are mirror images.
BELL, /12 & SHELF buttons present on LF and HF sections, intercancel and allow additional curve characteristics to be selected. These are 12dB/Octave filters and shelving EQ.
Q control knobs allows continuous control of the Q value for sections performing bell or band pass function.
FREQ(uency) knobs rovide continuous control of the centre frequency for band pass functions and turnover frequency for shelving and filtering functions.
Reverb Principles
Artificial reverberation models tend to fall into two main categories, which can be described as convolution and reflection simulation modelling. Both processes seek to achieve a degree of realism and virtual space by modelling room characteristics. The convolution model achieves this by recording the actual impulse response (due to reflections and dispersion) of existing spaces and imposing the resulting transfer characteristic on to the programme to reproduce the character of the space. However this model does not lend itself easily to the user interaction required for the artistic creation of reverberation effects that are commonly needed in production. Another important factor is that the user cannot readily simplify a convolution to avoid conflicts that often occur between the recorded ambience and the simulated reverb.The Sonnox Oxford Reverb belongs to the reflection simulation model as this allows the wide and varied user control intended from this device, in the pursuit of a high degree of artistic interaction and creative freedom.
Operation
Generally speaking simulation models employ two sections to generate spatial effects. The first section produces the early reflections that we use to perceive the dimensional space of environments and a reverb tail section is used to produce the longer term diffuse tails that occur in real environments, when the reflection complexity has become so dense that it is no longer possible to discern discrete events.It is the combination of the effects of these two sections that create the impression of space, environmental timbre and texture. One useful way to regard this is that the early reflections create a kind of ‘wire frame' model that we lock on to in order to fix the dimension of the space and the reverb tail forms the ‘plaster' that fills in the model and gives the space volume and long term character.
Adjustment Procedure
The Sonnox Oxford reverb provides for a very large degree of parameter control so that the professional user has the facility to produce reverberation ranging from subtle ambience and dry spaces all the way up to making dramatic sound effects. To get this degree of user facility a significant number of controls need to be present on the GUI panel.Although this may seem daunting initially, with experience the nature of the controls and the sonic effects they produce should quickly become self-evident. The best method to gain this experience is to simply operate it, taking note of the effect that results from varying control parameters. Indeed, it is intentional in the design of this application that the user should interact with it freely in order to create exemplary results in the normal course of its daily use, which uniquely match the artistic requirements of the particular production in progress at the time.
It is fully appreciated that during the modification of an existing set-up or the building of a new sound from scratch, the dividing line between something that is just ‘ok' and something that is exactly ‘perfect' is often very subtle and subject to the artistic requirements of the production and the environment in which it has been recorded or produced. The finer detail of the set-up procedure should therefore remain at the sole discretion of the user and should not be limited by existing set-ups or any particular doctrine.
Realistic Room Simulation Example
Most realistic room space simulations will consist of a mixture of appropriate early reflections and reverb tail. However the control set provided in the Sonnox Oxford reverb allows many ways to achieve a wide range of artistic effects that will suit a great many situations, many of which may involve almost completely opposing approaches. Experimentation is the key to mastering these and therefore the following procedures should be viewed as initial guidelines for familiarisation purposes only.Early Reflection Set-Up
A good method to achieve the correct balance is to listen to the early reflections first by setting the REVERB MIX fader to the ER position and adjusting the WET/DRY setting for a comfortable mix.At this point you should have an early reflection sound that produces a realistic perception of space, but may lack long-term reverberation and complexity.
Some additional important points regarding the Sonnox Oxford early reflections processing:
Reverb Tail Set-Up
The major difference between the early reflection processing and the reverb tail is that the latter contains no geometrically based dimensional information. Being constructed of mutually unrelated terms, it is designed to generate almost characterless spectral diffusion and spatial dispersion. Therefore its main purpose is to reiterate the sonic character and spatial cues provided by the input programme and the early reflection processing, with the minimum of disturbance throughout its decay period.However nuances in the way this is achieved play important roles in the resulting texture, timbre and spatial quality we perceive in the reverberation effect. Rather than providing the user with either a fixed model or a limited selection of algorithms, the Sonnox Oxford reverb offers full control over the parameters that most affect the sonic character of the reverb tail. This provides the user with the maximum creative facility.
Tail Mix Section
The first thing is to decide what drives the reverb tail section.Generally there is a mixture of two approaches to driving the reverb tail section we can consider. Either we want to carry the character of the early reflections into the reverb tail. Or we want to just add reverberation to the input signal so that the character of the input programme is carried into the reverb tail.
In practice we almost always need a mixture of both of these depending on the desired result.
The REVERB TAIL section of the GUI controls this function by providing the ability to mix, the output of the early reflections processing with the input signal and a delayed version of the input signal. Therefore it is possible to create a mixture of all three signals, any combination, or just a single source.
The delayed input signal controlled by the COMP DELAY function is normally set in ER TRACK mode so that the input drive to the reverb tail largely coincides with the initial output signals from the early reflection section. The following is a suggested way to set up the reverb tail.
Blending Early Reflections & Reverb Tail
Blending the early and late portions of the reverb is basically a matter of taste and suitability to the programme and mix.Some additional important points regarding the Sonnox Oxford reverb tail processing:
Equalisation
Equalisation of the reverb signal contribution is included to affect changes in the overall character of the simulation, either in response to artistic need or to enhance the realism of real space simulations.Almost all real environments exhibit complex frequency response characters that are generated by the reflection timing of the room spaces and objects within the area. The actual perceived frequency response is highly dependant on the position of the sound sources and the listener within the space.
Much of the most complex frequency response character is generated by the early reflections processing within the reverb application, but because simulation models have a reduced quantity of reflection nodes in comparison to real spaces, much of the overall resonance and tonal character may be absent from the total simulation.
Whilst the clean, unobtrusive nature and reduced tonal interference of the simulation reverb often blends more effectively in music production, post production and Foley situations often require an accentuated realism and much of this is provided by the overall frequency character of the spaces. Indeed this partially explains the success of convolution reverbs in the post production field.
All of the set-up examples contained in the Post category are examples of combinational reverbs which use equalisation to enhance the realism of spaces by providing the resonance's and response aberrations one would associate with the simulated spaces.
Equalisation Set-Up
Because the response of the reverb section is more unpredictable and fragile than the EQ, it is generally better to achieve a convincing set-up for the main reverb before starting out on any equalisation.Reverb EQ Destined for Music Production
For music production the role of the EQ is mainly that of subtle modification to the overall sound. This often entails reducing intrusive low frequencies, providing tonal matching within the mix or creating sound effects by accentuating reverberation within various registers of the musical ranges. Equalisation may also allow the reduction of unwanted artefacts due to the ‘run-on' of resonances within the programme, particularly in percussive sounds.As an artistic tool equalisation can be used to create a wide variety of effects limited only by the engineer's imagination and experimentation is definitely to be encouraged.
Reverb EQ Destined for Post Production.
For post production effects and simulation of real spaces the EQ serves to accentuate or even insert tonal aberrations that we associate with particular spaces. Often we don't notice these aberrations when we are actually in the spaces, but when adding simulations to dry sounds in a post production environment their absence can be a real limitation to effectiveness. There is no hard and fast way to achieve successful results, as there are several possible approaches to the problem. The following are presented as helpful hints.


