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# Super Nintendo Entertainment System (SNES)/Super Famicom
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the successor to NES to compete with Genesis, packing superior graphics and sample-based audio.
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its audio system, developed by Sony, features a DSP chip, SPC700 CPU and 64KB of dedicated SRAM used by both.
this whole system itself is pretty much a separate computer that the main CPU needs to upload its program and samples to.
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Furnace communicates with the DSP directly and provides a full 64KB of memory. this memory might be reduced excessively on ROM export to make up for playback engine and pattern data. you can go to window > statistics to see how much memory your samples are using.
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some notable features of the DSP are:
- pitch modulation, meaning that you can use 2 channels to make a basic FM synth without eating up too much memory.
- a built in noise generator, useful for hi-hats, cymbals, rides, effects, among other things.
- per-channel echo, which unfortunately eats up a lot of memory but can be used to save channels in songs.
- an 8-tap FIR filter for the echo, which is basically a procedural low-pass filter that you can edit however you want.
- sample loop, but the loop points have to be multiples of 16.
- left/right channel invert for surround sound.
- ADSR and gain envelope modes.
- 7-bit volume per channel.
- sample interpolation, which is basically a low-pass filter that gets affected by the pitch of the channel.
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Furnace also allows the SNES to use wavetables (and the wavetable synthesizer) in order to create more 'animated' sounds, using less memory than regular samples. this however is not a hardware feature, and might be difficult to implement on real hardware.
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# effects
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- `10xx` : set waveform.
- `11xx` : toggle noise mode.
- `12xx` : toggle echo on this channel.
- `13xx` : toggle pitch modulation.
- `14xy` : toggle inverting the left or right channels (x: left, y: right).
- `15xx` : set envelope mode.
- 0: ADSR.
- 1: gain (direct).
- 2: linear decrement.
- 3: exponential decrement.
- 4: linear increment.
- 5: bent line (inverse log) increment.
- `16xx` : set gain (00 to 7F if direct, 00 to 1F otherwise).
- `18xx` : enable echo buffer.
- `19xx` : set echo delay
- goes from 0 to F.
- `1Axx` : set left echo channel volume.
- this is a signed number.
- 00 to 7F for 0 to 127.
- 80 to FF for -128 to -1.
- setting this to -128 is not recommended as it may cause echo output to overflow and therefore click.
- `1Bxx` : set right echo channel volume.
- this is a signed number.
- 00 to 7F for 0 to 127.
- 80 to FF for -128 to -1.
- setting this to -128 is not recommended as it may cause echo output to overflow and therefore click.
- `1Cxx` : set echo feedback.
- this is a signed number.
- 00 to 7F for 0 to 127.
- 80 to FF for -128 to -1.
- setting this to -128 is not recommended as it may cause echo output to overflow and therefore click.
- `1Dxx` : set noise generator frequency (00 to 1F).
- `20xx` : set attack (0 to F).
- only in ADSR envelope mode.
- `21xx` : set decay (0 to 7).
- only in ADSR envelope mode.
- `22xx` : set sustain (0 to 7).
- only in ADSR envelope mode.
- `23xx` : set release (00 to 1F).
- only in ADSR envelope mode.
- `30xx` : set echo filter coefficient 0.
- `31xx` : set echo filter coefficient 1.
- `32xx` : set echo filter coefficient 2.
- `33xx` : set echo filter coefficient 3.
- `34xx` : set echo filter coefficient 4.
- `35xx` : set echo filter coefficient 5.
- `36xx` : set echo filter coefficient 6.
- `37xx` : set echo filter coefficient 7.
- all of these are signed numbers.
- 00 to 7F for 0 to 127.
- 80 to FF for -128 to -1.
- make sure the sum of these is between -128 or 127.
- failure to comply may result in overflow and therefore clicking.
