Introduction

The Sonnox Oxford Reverb plug-in is a highly flexible artificial reverberation generator, designed to complement existing Sonnox Oxford applications in providing the professional user with highest technical and sonic performance, coupled with high levels of artistic and creative capability.

By avoiding fixed algorithms, and providing user control of all parameters including comprehensive equalisation functions, the Oxford Reverb provides the professional engineer with a powerful facility to build virtual spaces freely, depending on artistic needs, ranging from dry reflection ambiences, room and hall simulations, sound effects, all the way to wide open reverberant spaces with a exceptionally large range of possible texture and spatial character.

Principles of Reverberation

Artificial reverberation models tend to fall into two main types, which can best 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 onto 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 model to avoid conflicts that often occur between the recorded ambience and the simulated reverb.

The Sonnox Oxford Reverb belongs to the reflection simulation type, 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.

Overview

Generally speaking, simulation models employ two sections to generate spatial effects. The first section produces the Early Reflections (see above) 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 Reflection section creates 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 the creation of dramatic sound effects. To achieve this degree of user facility, a significant number of controls need to be present on the ‘front 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 the plug-in, 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 setup 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 setup procedure should therefore remain at the sole discretion of the user, and should not be limited by existing setups or any particular doctrine.

Realistic Room Simulation

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 Setup

A good method to achieve the correct balance is to listen to the Early Reflections first by setting the REVERB MIX fader to its ER position, and adjusting the WET /DRY fader for a comfortable mix (both these controls are in the plug-in’s OUTPUT section).

Start with a neutral setting, with WIDTH and TAPER in their mid position, FEED ALONG and FEEDBACK at minimum, and LF ROLL-OFF (in the INPUT section) at minimum (mostly HF content).

It should now be possible to perceive the space changing when you adjust the SIZE control. Initially, set this to something appropriate.

Toggle through the SHAPE selection buttons, noting the difference between them, and decide on one that most suits what you are looking for.

At this point the FEED ALONG setting can be increased, noting the effect it has on overall complexity in the reflections and the timbre of the space. For realistic spaces, settings around the mid position are often best, but experimentation of the full range is encouraged.

Listening carefully to the resulting reflections, adjust the FEEDBACK fader with the PHASE SELECT button selected (the default), to introduce some reiteration into the space, noting that the space becomes more resonant and the reflections more diffuse. Without feedback, the reflections will end abruptly when they are finished. This is useful for creating dry spaces often appropriate for percussion tracks. However, for realistic spaces, an amount of feedback is required to produce a more natural dispersion and timbre. Too much feedback will result in ringing effects, which can be particularly intrusive for smaller spaces.

To give the space a realistic absorption and frequency response character, start increasing the LF ROLL-OFF control to tailor the HF response caused by the reflections over time. There is no fixed rule for what works best, and creative freedom should take precedence. However, generally speaking, larger spaces require greater absorption settings than small spaces, since a major cause of absorption in real spaces is the distance that the sound travels in air.

The WIDTH and TAPER controls can now be adjusted to give an appropriate stereo spread and reflection character to the simulation. Some interplay between the FEED ALONG and the TAPER controls may be required to arrive at the best overall sound character, as both can give the effect of increasing the prominence of the reflections.

At this point it is worth adjusting the POSITION fader to determine the listening position within the virtual space. It should be possible to perceive the effect of entering the space as the setting moves off the back wall (minimum setting) into the virtual space. It is important to bear in mind that the primary reflection from the back wall can get quite fast in smaller spaces if the position is too far forwards, so although the simulation may sound correct when 100% wet, frequency combing effects may occur when it eventually gets combined with the dry signal in a mix. Generally speaking, simulations with the source and destination at the back wall (minimum setting) will always survive the addition of the dry signal, but under some circumstances, forward settings may not. Therefore it is safest to start with the POSITION at minimum initially, and make any adjustments while using the reverb in a mix situation.

Finally, it’s a good idea to run through all the settings, making final adjustments by offsetting one parameter against another in order to get precisely the result that sounds best with the programme material. Bear in mind that very often very small changes can make the difference between something stunningly good or just average!

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.

Additional Important Points on Early Reflections Processing

It is sometimes useful to use an early reflection model on its own (without any Reverb Tail) where significant environmental reverberation already exists on the recorded track to be treated. In this case, the recorded reverb can often be included within the simulated space without conflict, giving the perception that the track was actually recorded in stereo.

The perception of large spaces can be alternatively constructed with relatively small SIZE settings, by the application of large amounts of FEED ALONG and FEEDBACK. While such sounds may produce less faithful emulations of real spaces, great sound effects and very dense general ambiences may be generated this way.

Moderate duration early reflections built using fairly small SIZE settings and large amounts of FEED ALONG with no FEEDBACK can be very useful for percussion ambiences, since they end abruptly and thus avoid creating intrusive ‘hubbub’ from reverb run on.

The effect of very large spaces with long Reverb Tails can be constructed with the Early Reflection processing alone, by using large SIZE settings, moderate FEED ALONG and large amounts of FEEDBACK. Although such spaces will be less diffuse than Reverb Tail models (because they always contain cyclic reflections), they are still very useful for creating the impression of extremely large spaces and generating rich sound effects.

The STEREO SEPARATION fader mixes left and right signals together at the input of the processing. This is useful where the virtual space is required to be fixed regardless of input programme panning. But when the programme is a viable stereo source (either panned or natural) better placement within the reverb sound field will be achieved with higher separation settings.

Reverb Tail Setup

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 TAIL MIX section of the ‘front panel’ controls this function by providing the ability to mix the output of the Early Reflection processing with the input signal, and a delayed version of the input signal. It is therefore 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 selected to ER TRACK mode so that the input drive to the Reverb Tail largely coincides with the initial output signals from the early reflection section.

Suggested Setup for the Reverb Tail

Set the ER MIX fader to its DRY position, the TAIL INPUT fader to its DLY INP position, and the COMP DELAY fader to its mid position. This ensures that the input drive to the tail section is the compensated version of the input signal. This is a good starting point as it is the character of the input that we need to address first.

Set the REVERB MIX fader to its central position so that you hear an equal contribution from the Early Reflection and Reverb Tail signals. This is useful because we are initially concerned with making the overall Reverb Tail match the timing requirements of the early reflection sound you have already made.

Set the OVERALL SIZE, DISPERSION and PHASE DIFF faders to their mid position. Set the PHASE MOD and ABSORPTION faders to their minimum position and DIVERSITY to its maximum position. This sets up a neutral starting point where the effect of controls will be most easily heard when we get to adjust them.

By increasing the REVERB TIME, the tail can be heard to extend to the period set on the control. Set this to something that matches the sound you are aiming for. At the moment the tail will sound rather grainy, and its stereo image will be largely in the centre of the sound field.

Moving the DISPERSION fader in a positive direction will result in increased complexity and smoothness in the longer term. The higher the setting, the faster the complexity builds over time. Set this somewhere that provides the required effect, bearing in mind that real reverberant spaces take a period of time to build complexity, especially if they are large and reflective.

Adjust the PHASE DIFF control and note that the tail image begins to spread across the stereo field. The higher the setting the quicker the spread will occur over time. Generally speaking, large settings are better in mix situations because they produce a wide sound field quickly. However, for very large spaces or sound effects, a slower spread from middle to sides can often produce a more realistic effect. The included setup ‘far away’ is a good illustration of this. It is also worth experimenting with negative PHASE DIFF settings, noting that the spatial effects build into far wider and more diverse stereo sound fields. Negative settings are often more effective when you are aiming for greater perceived immersion within the simulated space.

Increasing the PHASE MOD control will provide a degree of variance for the above settings (as though you were moving the PHASE DIFF control slowly). This provides a larger degree of realism to the Reverb Tail because it prevents it from becoming spatially static. It keeps your attention on the reverberation because it changes subtly over time – much as in real spaces where natural movement of the air or objects within the space continually modify its characteristics.

To give the space a realistic high frequency profile over time, ABSORPTION should be applied in the same manner as in the ‘early reflection’ settings. In general, larger spaces require greater absorption, however some larger spaces can reflect considerable HF from the their back extremities. It is important to bear in mind that allowing a large HF content in the Reverb Tail may accentuate unnaturally strident or harsh sounds, particularly if there are sustained HF components in the programme or there is prominent resonance in the Early Reflection stages.

The overall spread of the reverb can be adjusted using the DIVERSITY fader. Reducing this control adds statistical weighting to the centre image, which is often needed to anchor the sound field to centre stage. It is important to consider the intended speaker layout while setting this control, since a large degree of left to right mixing occurs acoustically in the listening environment. It is particularly important to remember that what appears a natural setting for this control will vary considerably between headphone and speaker listening methods!

Blending Early Reflections and Reverb Tail

Blending the early and late portions of the reverb is basically a matter of taste and suitability to the programme and mix.

Adjust the REVERB MIX control to fine-tune the contribution from both the sections. Generally speaking, the application of more late Reverb Tail energy will result in a softer and more diffuse reverberation at the expense of spatial realism.

Now your effort is to decide what proportion of the Early Reflection mix will be included in the Reverb Tail input. This is particularly crucial since the whole long-term character of the reverb is affected. Advancing the TAIL INPUT fader away from DLY INP towards the ER MIX position will progressively allow more signal drive from the Early Reflection mix stages into the tail section. Generally, there is normally a need for some Early Reflection signal in the Reverb Tail, however this is not a ‘rule’ and the amounts required are most often quite small. Too much early reflection drive to the tail may cause unwanted ringing or boominess from the Early Reflection section to become intrusive in the longer term. Too little drive may make the tail lack character. It is all a question of settings, programme source parameters and artistic taste. Experimentation is everything!

Throughout the blending process it is a good idea to go back periodically and adjust the Reverb Tail OVERALL SIZE parameter in order to get the best timbral blending between the sections. The overall size parameter can be adjusted all the way from what sounds like a ‘cymbal resonating’ to a wide open space — without affecting the decay time, so there is great deal of latitude in what can be achieved. In general there is a trend for larger Early Reflection spaces to most suit larger Reverb Tail overall sizes, because they exhibit a slower build up of complexity. However this is not a rule — in practice, very subtle changes in the overall size can result in exemplary realism when resonance within the Early Reflections and Reverb Tail sections complement each other.

Application of the LF ROLL-OFF control should only be attempted after an overall reverberation sound has been achieved, as low frequency spatial cues are very important to our perception of natural spaces. In the event that the reverb produces excess LF energy (particularly if the simulation space is very small), or an effect is desired which favours only HF programme content, LF ROLL-OFF can be applied with discretion, depending on the overall requirement of the programme.

Additional Important Points on Reverb Tail Processing

Since the Reverb Tail is essentially neutral, containing no dimensional character, it can be used by itself with very low reverb times to produce general ambiences and ‘characterless’ Reverb Tail. In particular, with small to moderate OVERALL SIZE settings, effects ranging from ‘boomy’ drum rooms to vocal double tracking and multiplication can be achieved.

If the programme consists of a stereo source that already contains significant environmental reflection, the Reverb Tail section can be used on its own to simply adopt the character of the original recording and extend the natural reverb within the recorded space.

The Reverb Tail processing consists of two separate sections for left and right signals, which under some conditions can perform entirely independently. If the Reverb Tail processing is used on its own with stereo panned sources (without any early reflection contribution), care should be taken to ensure that the STEREO SEPARATION and DIVERSITY controls are not both set to maximum, as this could result in a left or right only reverb signal if the source is panned hard to either side.

Equalisation

Equalisation of the reverb signal contribution is included in this comprehensive plug-in to effect 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 characteristics that are generated by the reflection timing of the room spaces and objects within the area. The actual perceived frequency response is highly dependent on the location of the sound sources and the position of the listener within the sound space.

A large part 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.

While the clean, unobtrusive nature and reduced tonal interference of simulated 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 simulated spaces. Indeed this partially explains the success of convolution reverbs in the post-production field.

All of the EQ setup examples contained in the Post-production category (see below) are examples of combinational reverbs that use equalisation to enhance the realism of spaces by providing the resonances and response aberrations one would associate with those spaces.

Equalisation Setup