TAP-plugins
Tom's Audio Processing plugins
for audio engineering on the Linux platform

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## TAP Reverberator

TAP Reverberator is unique among reverberators freely available on the Linux platform. It supports creating no less than 43 reverberation effects, but its design permits this to be extended even further by the user, without doing any actual programming. Please take a look at TAP Reverb Editor, a separate JACK application for more information about this.

The design is based on the comb/allpass filter model. Comb filters create early reflections and allpass filters add to this by creating a dense reverberation effect. The output of the set of comb and allpass filters (also called the reverberator chamber) is processed further by sending it through a bandpass filter. The resulting band-limited reverberation is very similar to the natural reverberation that occurs in acoustic rooms. To achieve an even more natural-sounding effect, all comb filters have high-frequency compensation in their feedback loop. This is to model that the reflection ratio of acoustic surfaces is the function of frequency: higher frequencies are attenuated more, and thus decay time of higher frequency components is significantly shorter.

To enhance the reverberation sound even further, a special option called Enhanced Stereo is provided. When turned on (which is the default), it results in an added spatial spread of the reverb sound. This feature is most noticeable when applying the plugin to mono tracks: the sound of these tracks will "open up" in space.

### General information

Unique ID | 2142
I/O ports | 2 inputs / 2 outputs
CPU usage (44.1 kHz) | 10.7% max. (see Notes)
CPU usage (96 kHz) | 24.8% max. (see Notes)
Hard RT Capable | No
In-place operation | Supported
run_adding() function | Provided

### Usage tips

Despite the rather complex algorithm of this plugin, usage is relatively simple and the user is required to adjust only a limited number of global controls. This is achieved by defining "presets" called Reverb Types which actually mean larger sets of internal control values. When choosing a Reverb Type, the plugin loads all values associated to that type, and operates according to the newly loaded values. (If you want access to the internals of a Reverb Type, please check out TAP Reverb Editor.)

The most important global variable of the whole effect is the decay time. By adjusting this, you can create the feel of a larger acoustic space (set the decay to more than 2-3 seconds for this), as well as a "tight", relatively dry effect (for which you should set a much lower value). But you should be aware of the fact that not every reverberation type sounds good at any decay setting (see the table below for recommended decay values). For example, a Room (Small) will not sound too good when you set the decay to a very large value, and vice versa, a Hall (Large) will not sound optimal at very small decay settings. However, when choosing a more artificial type of reverberation (Afterburn, Pulse Chamber (Reverse) or Warble Chamber, for example), there is no "natural" decay time: set it as you see fit according to the effect you are trying to achieve.

General advice about adjusting the dry and wet signal levels: the wet level should be about 3 to 15 dB lower than the dry level, according to the reverb type you are using. Of course if you want to create an artificial sounding effect, you can decrease the dry level, even down to -70 dB if that is what you want. However, one thing to know is that you shouldn't set the wet level to a very high value (generally not above 0 dB) because the output level of the plugin may become too high and you may overdrive the next plugin in the chain, or you may cause signal clipping in the master output of your multitrack. Furthermore, because the wet signal is added to the incoming dry signal, you should decrease the dry level as well by a few dB-s (and then set the wet level according to this) so as not to raise the overall loudness of the track.

Usually, when trying to create a natural-sounding reverberation effect, all components (comb filters, allpass filters, the bandpass filter and the stereo enhancement mode) should be switched on. However, to create artificial effects, it is possible to turn off any of these components. For example, if you only want the sound of multiple echoes, you can turn off everything but the comb filters; if you want to create a more unnatural, harsh effect, turn off the bandpass filter processing. (Also note that bandpass filters of different Reverb Types have different low and high cutoff frequencies, since this filtering also affects the nature of the reverberated sound very much.) Naturally, components that are switched off don't consume CPU power.

As mentioned earlier, not all Reverb Types sound good with any decay setting. The following table contains decay time settings adequate for particular Reverb Types. Decay times are shown in seconds. As a rule of thumb, when decay times are above 3 seconds, the "Wet Level" should be at least 6 or more decibels below the "Dry Level". The values below are only general advice, and they are provided merely as a starting point for your experimentation. You are free to use any value that sounds good for your mix.

### Recommended decay times

Reverb Type | Decay Time
--- | ---
AfterBurn | 2.8
AfterBurn (Long) | 4.8
Ambience | 1.1
Ambience (Thick) | 1.2
Ambience (Thick) - HD | 1.2
Cathedral | 10
Cathedral - HD | 10
Drum Chamber | 3.6
Garage | 2.3
Garage (Bright) | 2.3
Gymnasium | 5.9
Gymnasium (Bright) | 5.9
Gymnasium (Bright) - HD | 5.9
Hall (Small) | 2.0
Hall (Medium) | 3.0
Hall (Large) | 5.1
Hall (Large) - HD | 5.1
Plate (Small) | 1.7
Plate (Medium) | 2.6
Plate (Large) | 5.7
Plate (Large) - HD | 5.7
Pulse Chamber | 3.1
Pulse Chamber (Reverse) | 3.1
Resonator (96 ms) | 4.0
Resonator (152 ms) | 4.2
Resonator (208 ms) | 5.1
Room (Small) | 1.9
Room (Medium) | 2.8
Room (Large) | 4.4
Room (Large) - HD | 4.4
Slap Chamber | 2.3
Slap Chamber - HD | 2.9
Slap Chamber (Bright) | 3.4
Slap Chamber (Bright) - HD | 3.7
Smooth Hall (Small) | 1.8
Smooth Hall (Medium) | 3.0
Smooth Hall (Large) | 5.9
Smooth Hall (Large) - HD | 5.9
Vocal Plate | 3.1
Vocal Plate - HD | 3.1
Warble Chamber | 4.0
Warehouse | 6.0
Warehouse - HD | 6.0

Q: What is that HD in the name of some Reverb Types?

A: HD stands for High Density. Reverb Types marked with this are enhanced versions of other types, for example Hall (Large) - HD is derived from Hall (Large). Enhancement means additional comb and/or allpass filters, which result in an even smoother reverberation effect. However, more filters mean more CPU usage, so it's up to you to decide whether to choose them or not. If CPU usage is not a great concern, it is recommended to use the HD versions where available.

### Summary of user controls

name | min. value | default value | max. value
--- | --- | --- | ---
Decay [ms] | 0 | 2500 | 10000
Dry Level [dB] | -70 | 0 | +10
Wet Level [dB] | -70 | 0 | +10
Comb Filters | OFF | ON | ON
Allpass Filters | OFF | ON | ON
Bandpass Filter | OFF | ON | ON
Enhanced Stereo | OFF | ON | ON
Reverb Type | 0 | 0 | 42

### Notes

The maximum number of filters is 20 combs and 20 allpass filters. Actually it is double this much because every filter exists in two instances for the two channels. This amount allows for the creation of very dense, very smooth-sounding Reverb Types.

Comb filters are implemented as first-order IIR filters with a biquadratic low-pass filter in the feedback loop, which has its cutoff frequency determined by the frequency response parameter of the comb filter. Allpass filters are implemented as ordinary first-order IIR filters.

When Enhanced Stereo is enabled, parameters of the two instances of the same filter are set to slightly different values. Without this option, the two input channels are processed in the exact same way. It is absolutely recommended to turn this on when applying the plugin to mono tracks, but it is also useful on stereo tracks.

Because the varying complexity of Reverb Types and the fact that options can be switched on/off individually, CPU usage is a function of user settings. For this reason, this plugin is not hard RT capable. The CPU usage was measured with all options turned on, and the Reverb Type set to Ambience (Thick) - HD, which is the most complex one at the moment. Other Reverb Types with fewer comb/allpass filters utilize proportionately less CPU.

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