Enhancement: Stereo Synthesis / Signal Path

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The current implementation is monaural. While the potential exists to expand the monaural signal into a stereo field using various effects, it would be much more interesting if stereo processing were introduced as a fundamental aspect of the underlying synthesis:

• Basic waveform generators to remain unchanged
• Wavetable generator could support separate left/right data.
• Pan Envelopes (-1.0 left, 0.0 centre, +1.0 right)
• Oscillators to have a single pitch control but expanded to have Pan and separate phase for left and right.
• SuperOscillator to support separate Pan for each harmonic on the stack.
• Operators expanded to include Pan Envelopes.
• Amplitude modulation to apply in stereo, e.g. separate left/right processing
• Phase modulation to apply in stereo, e.g. separate left/right processing

[0xABADCAFE]

This work will likely require that the currently ubiquitous notion of a Packet is extended into include a stereo variant which has the same number of sample pairs.

• Stereo Packets shall be used for all audio signals
• Monaural Packets should be used for control signals
• Stereo and Monaural Packets should be inter-operable by basic channel duplication for mono to stereo and channel averaging for stereo to mono

[0xABADCAFE]

http://www.cs.cmu.edu/~music/icm-online/readings/panlaws/

• Add a PanLaw interface in the Signal namespace
• Converts single channel control Packets of normalised panning data (-1.0 ... 0.0 ... 1.0) to a stereo Packet of attenuation values for left and right.
• Provide implementation based on established linear and equal power panning models.

[0xABADCAFE]

Considering the effects of equal power panning on mono signals, the implications for stereo phase modulation are complex and a bit unintuitive.

• Centre panned mono signals would have half the intensity (for linear pan) of an equivalent single channel mono signal. For a modulator this reduces the modulation intensity.
• Full intensity is reached for left or right only at extreme pan.
• Fine for outputs but weird for phase modulation
• Consider a separate Pan Law for modulator outputs that have a clamped maximum intensity at the centre and panning right is just attenuating the left (and vice versa)
• This would ensure that the current modulation index behaviour is respected at centre pan.

[0xABADCAFE]

While not necessarily the "cleanest" approach, there are some implementation benefits to be had from allowing the existing Packet class to be monaural or stereo, rather than explicitly creating a StereoPacket extension. TBC.