Voltage Controlled Oscillator With Wave Shaping
Most audio frequency oscillators generate a range of periodic waveforms. In general, these waveforms contain a large number of harmonics and are suitable for use as the basis of subtractive synthesis, wherein harmonics are removed or emphasised to create new sounds. (Some oscillators also produce aperiodic waveforms which are perceived as noise, but the RS Integrator has a dedicated module for this.)
These oscillators are the prime sound sources within a synthesiser. There are other sources - such as self-oscillating filters - but for the majority of applications the initial sound will be generated by one or more conventional oscillators. It is therefore vital that these offer accurate waveforms, are stable with respect to pitch, and that they suffer from a minimum of unwanted noise and/or distortion. They should also be very flexible, which means that they must be capable of producing a wide range of timbres. Finally, they must exhibit one further, but unquantifiable quality: they must sound good.
You may think that it would be straightforward to satisfy these criteria. Unfortunately, it isn't, and many synthesisers suffer from a "weak" or "characterless" sound. And, since analogue synthesis is subtractive you can't put back what wasn't there in the first place. The oscillator itself must be of the highest possible quality. Which leads us to the RS90...
The primary method of controlling the pitch is by applying a suitable CV to the CV IN socket. This respond correctly to the 1V/oct standard adopted by Moog, ARP, Roland and Sequential Circuits (among others). It will not allow you to play conventional melodies if you apply a CV conforming to the Hz/Volt standard used by Yamaha and most Korg monosynths.
Before leaving the factory, every RS90 is calibrated to respond linearly to input control voltages ranging from -10V to +10V. This gives the RS90 a theoretical audio range of 20 octaves. In practice, the range is closer to a "mere" 16 octaves - still far exceeding the capabilities of most other manufacturers' devices.
A CV of +2.5V will generate a 0% leading pulse wave;
A CV of 0V will generate a square wave;
A CV of -2.5V will generate a 0% trailing pulse wave. The output from the SQR-OUT socket is approximately ±5V.
The sawtooth wave output can be adjusted from a falling sawtooth through a triangle wave to a rising sawtooth waveform as you turn the SAWTOOTH SHAPE control from its fully anticlockwise position through to its most clockwise position. As factory calibrated, the triangle shape will be obtained when the knob is at "12 o'clock". You can also influence the sawtooth wave shape by applying a CV to the CV-IN SHAPE socket next to the SAWTOOTH SHAPE control, as follows:
A CV of
+2.0V will generate a falling sawtooth wave;
The output from the SAW-OUT socket is -2V to +8V when a true sawtooth wave is produced, and ±2.5V when a triangle wave is produced.
The SYNC IN socket will accept voltages in the range ±10V, but the sound produced by syncing the RS90 to an external source depends upon a wide range of factors. These include the level of the sync source, its frequency, its waveform, and its polarity.
For a 'hard' sync sound (as produced, for example, by the Moog Prodigy and Moog Source) you should apply a square- or pulse- wave that crosses 0V. For best results the sync source should be at a lower frequency than the RS90 it is modulating.
the RS90 as a simple tone generator