Source:Electronic Music Studios, London, England (undated)
EMS Pitch-To-Voltage Converter(with Built-In Voltage Controlled Sawtooth Oscillator and Envelope Follower). Illustrated, descriptive one page product sales sheet. Description of how this circuit works. "The primary function of this device is to convert an audio input into a DC voltage whose value is proportional to the pitch of that input signal. If this voltage is then applied to the control input of of an oscillator, the oscillator can be tuned to follow the input in unison or at any other interval desired..."