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EMS Pitch-to-Voltage Converter

EMS Data Sheet

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The EMS Range of Ancillary Studio Modules EMS Modules are designed not only for use with Synthi synthesisers but with any complex of voltage controlled equipment, of whatever manufacture. They are supplied in handsome afrormosia cases, but can be removed and mounted in standard 19" racks, occupying only 1.7" (44mm) of vertical space. They contain their own mains power unit with a very wide range of stabilization to cope with poor mains line conditions, being operable at anything from +10% to more than—23% of nominal line voltage. Connections to and from the modules can be made either from the jack sockets on the front panel or via the multi-way socket at the back.


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 an oscillator, the oscillator can be tuned to follow the input in unison or at any other interval desired. In situations where musicians are already using synthesisers to treat the sound of instruments, voice or tape, the addition of the Pitch-to-Voltage Converter introduces a range of possibilities hitherto unexplored, since it enables direct control of the synthesiser's parameters from a live musical input.

In order to use the instrument correctly it is important to understand the considerable problems which had to be solved to make the P-VC possible at all. (1) The circuit has to detect as quickly as possible what the input pitch is — our ears, for example, require on average 13mS to know what note it is, and less than this sounds like a pitchless click. The P-VC does this not by the normal method of comparing the number of zero-crossings with a known period of time, but by measuring the actual period of the signal, which gives a very much quicker answer. (2) Most musical notes are rich in harmonics—i.e. are not one pitch but several or many. To make matters worse, the fundamental is often quite weak. Nevertheless the P-VC must "find the fundamental" in order to decide what pitch to follow. A special "adaptive filter" ensures that the instrument tracks if the fundamental comprises 10% or more of the total signal energy, the filter always seeking the lowest pitch present. It is best, however, to use inputs of clear pitch and reasonably constant level. Electronic inputs can be easily adjusted for perfect pitch following. (3) Most musical sounds are discontinuous— i.e. each pitch is attacked and has a characteristic envelope, and there may or may not be complete silence between notes. The P-VC detects and follows this envelope, and also the attack at the beginning of a note. The output can be made to contain a facsimile of the original input envelope, or a new shape of envelope, or both. It will also generate inverted signals if required.

Outputs from the Pitch-to-Voltage Converter are simplified into two main channels, one being used for signals and the other for control voltages, although each individual output is also available on the front panel. The signal channel gives a manually preset mixture of original input signal with a tuneable internal oscillator which tracks the input both in pitch and loudness. The control voltage output is selected by a switch to give either a pitch-following or an envelope-following (loudness) output, the latter of which can obey either a linear or a logarithmic law. As stated above, this Channel 2 mode selection switch also gives any of these voltages in an inverted form.

Accurate tuning of the device and any synthesiser with which it is used is made simple by the inclusion of a reference oscillator which provides a test tone input, with a switch to raise its pitch exactly one octave. This will ensure that the output signals and voltages bear the correct relationship to the input.

The Pitch-to-Voltage Converter also delivers an envelope triggering pulse of either of two types. "Hold On" gives an output all the time the input signal exceeds the trigger threshold level. "One Shot" gives a 20mS (approx.) pulse every time the input level rises to the threshold. The unit accepts inputs from acoustic instruments through a microphone, and electric guitar, tape recorder or any electrical instrument by direct input. Inputs of indefinite pitch, such as drums, will not convert satisfactorily though interesting random effects can be obtained. If presented with a chord, the device will choose the lowest note.

For a considerable time pitch-to-voltage conversion has been the missing link in the production chain of synthesised sound — the connection between the actual sound or the signal outputs of electrical devices, and the control inputs of oscillators and other voltage controlled circuits. Many musicians are already reaping the benefit from the introduction of this unique product.


Power Supply:
240 or 115VAC 50/60Hz +10% to —23%

Signal Inputs:
Min. permissible levels for gate operation—
Low Range: 10mV p-p; High Range: 100Vp-p
Max. permissible levels—
Low Range: 100mV p-p; High Range: 1V p-p

Signal Output:
18V p-p max.

Noise and Hum:
—60dB referred to max. output level.

Modulator Distortion:
10% max.

Pitch Voltage:
1V (+/- 0.15V) per octave ( invertible) .

Envelope Voltage:
1V (+/- 0.15V) per 6dB gain (log. or lin., both invertible).

Trigger Out:
Average +4V, max. unloaded 12V

Internal Oscillator:
f=256Hz +/- 24%. 2f=perfect octave of f. (no guarantee of actual pitch of oscillator, which is not important, but octave perfectly true ).

Facilities Socket:
All jack sockets are duplicated on this multi-way socket except EXC. MOD., since the disconnection of the oscillator is by insertion of jack.

Electronic Music Studios (London) Limited
277 Putney Bridge Road London SW15 2PT
Telephone 01. 788 3491/2 Telex 92 83 72
New York: Suite 2222 110 East 59 Street NY 10022
Telephone 212 832 3115 Telex 42 40 33
New Address: 1977: C/o Peter Zinovieff, The Priory
Great Milton, Oxford
Telephone 08446-729

Data Sheet (Optically Character Read) from The Terrey Collection Library

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