EVOC 20 PolySynth Sidechain Analysis Parameters

The parameters in the Sidechain Analysis section control how the input signal is analyzed and used by the EVOC 20 PolySynth. You should be as precise as possible with these parameters to ensure the best possible speech intelligibility and accurate tracking.

Figure. Sidechain Analysis parameters.
  • Attack knob: Determines how quickly each envelope follower—coupled to each analysis filter band—reacts to rising signal levels. Longer attack times result in a slower tracking response to transients—level spikes—of the analysis input signal. A long attack time on percussive input signals—a spoken word or hi-hat part, for example—will translate into a less articulated vocoder effect. Therefore, you should set the Attack parameter to the lowest possible value to enhance articulation.
  • Release knob: Determines how quickly each envelope follower—coupled to each analysis filter band—reacts to falling signal levels. Longer release times cause the analysis input signal transients to sustain for a longer period at the vocoder’s output. A long release time on percussive input signals—a spoken word or hi-hat part, for example—will translate into a less articulated vocoder effect. Use of extremely short release times results in rough, grainy vocoder sounds. Release values of around 8 to 10 ms are useful starting points
  • Freeze button: This parameter, when enabled, holds—or freezes—the current analysis sound spectrum indefinitely. While Freeze is enabled, the analysis filter bank ignores the input source, and the Attack and Release knobs have no effect. See Freezing the EVOC 20 PolySynth’s Input Signal.
  • Bands field: Determines the number—up to 20—of frequency bands that are used by the filter banks. See Setting the Number of EVOC 20 PolySynth Filter Bank Bands.

Freezing the EVOC 20 PolySynth’s Input Signal

The Freeze button in the Sidechain Analysis section of the EVOC20 PolySynth freezes the sound spectrum of the analysis input signal.

Figure. EVOC 20 Polysynth Freeze button.

By freezing the input signal you can capture a particular characteristic of the signal, which is then imposed as a complex sustained filter shape on the Synthesis section. Here are some examples of when this could be useful:

  • If you are using a spoken word pattern as a source, the Freeze button could capture the attack or tail phase of an individual word within the pattern—the vowel a, for example.

  • If you want to compensate for people’s inability to sustain sung notes for a long period, without taking a breath, you can use the Freeze button. If the synthesis signal needs to be sustained but the analysis source signal—a vocal part—is not sustained, use the Freeze button to lock the current formant levels of a sung note, even during gaps in the vocal part, between words in a vocal phrase. The Freeze parameter can be automated, which may be useful in this situation.

A Short Primer on Formants

A formant is a peak in the frequency spectrum of a sound. When the term is used in relation to human voices, formants are the key component that enables humans to distinguish between different vowel sounds—based purely on the frequency of these sounds. Formants in human speech and singing are produced by the vocal tract, with most vowel sounds containing four or more formants.

Setting the Number of EVOC 20 PolySynth Filter Bank Bands

The Bands field in the Sidechain Analysis section determines the number of frequency bands the EVOC 20 PolySynth’s filter bank uses.

Figure. EVOC 20 Polysynth Bands field.

The greater the number of frequency bands, the more precisely the sound can be reshaped. As the number of bands is reduced, the source signal’s frequency range is divided up into fewer bands—and the resulting sound will be formed with less precision by the synthesis engine. You may find that a good compromise between sonic precision—allowing incoming signals such as speech and vocals to remain intelligible—and resource usage is around 10 to 15 bands.