ESP-20 Processor

The Cherry Audio ESP-20 Processor recreates the slightly bizarre and endlessly useful External Signal Processor section of the classic MS-20 synthesizer. ESP-20 analyzes incoming audio and generates matching voltages for controlling oscillator pitch and envelope amplitude, letting you "play" Voltage Modular by singing, playing guitar, or any other monophonic signal source. ESP-20's frequency converter has a much wider range than the original for increased functionality, while still retaining the inherent quirkiness. 

Inputs, Outputs and Controls

In jack- Plug audio signals in here. 

Signal Level, Overload LED- Attenuates or amplifies incoming signal levels (up to +6 db) for optimum tracking performance; experiment with signal input level if tracking isn't working as desired. The overload (OL) LED illuminates if the input signal is too loud. 

Amp output jack- The Out jack beneath the Amp icon outputs the the post-Signal Level audio. 

High Cut Freq- This is a 12db per/octave, non-resonant lowpass filter and forms half of the Band Pass Filter block. Its intended use is to remove extraneous high frequencies in order to aid in pitch tracking. 

Low Cut Freq- This is a 12db per/octave, non-resonant highpass filter and forms the other half of the Band Pass Filter block. Its intended use is to remove extraneous low frequencies in order to aid in pitch tracking. 

Band Pass output jack- Though the aforementioned lowpass and highpass filters aren't necessarily intended for modifying audio signals, you're free to use them this way - the Band Pass output jack outputs the post filter(s) signal. 

Threshold- This sets the level at which a 5V gate (constant) or trigger (instantaneous) voltage is output at the Gate Out and Trig Out jacks, respectively. Threshold has no effect on the Env Out jack voltage

CV Offset- Adds or subtracts up to 5V to the Freq>Volt CV Out jack. Typically this would be used as a tuning or transpose control when patched to an oscillator CV input. It's generally advisable to begin with CV Offset at the 0V position (remember that right-clicking a knob and selecting Return To Default Value is a quick and accurate shortcut).

Freq>Volt CV Out jack- Outputs the pitch CV derived from the incoming signal, as well as any offset voltage added with the CV Offset control. This generally will be patched to an oscillator's Keyboard CV or Pitch CV input. 

Env Out- Outputs a continuous, dynamic voltage corresponding to the ESP-20 input signal level. The Signal Level knob will help to dial this in. 

For more consistent CV dynamics, patching the input signal through a compressor module prior ESP-20's input can be helpful. (A third-party VST/AU compressor or limiter plug-in can optionally be used in conjunction with a Plug-In Host module.) 

Gate Out and LED indicator- Outputs a constant 5V gate signal, dependent on the Threshold knob setting. The LED next to it lights to indicate when a 5V gate voltage is present. 

Trig Out and LED indicator- Outputs a very brief 5V trigger signal (1ms in length), dependent on the Threshold knob setting. The LED next to it flashes to indicate when a 5V trigger voltage is present. 

The Trig Out jack may output constant triggers if the Threshold knob setting is right on the edge of triggering. We're pretty sure this is called "hysteresis" - if this happens, a little tweak to the Threshold knob setting will fix it.