51 lines
3.1 KiB
Markdown
51 lines
3.1 KiB
Markdown
# Super NES
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The successor to NES to compete with Genesis. Now packing superior graphics and sample-based audio. Also known as Super Famicom in Japan.
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Its audio subsystem, developed by Sony, features the DSP chip, SPC700 microcontroller 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. As of version 0.6pre2, 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:
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- It has pitch modulation, meaning that you can use 2 channels to make a basic FM synth without eating up too much memory
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- It has a built in noise generator, useful for hihats, cymbals, rides, sfx, among other things.
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- It famously features per-channel echo, which unfortunately eats up a lot of memory but can be used to save channels in songs.
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- It can loop samples, but the loop points have to be multiples of 16.
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- It can invert the left and/or right channels, for surround sound.
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- It features ADSR, similar to the Commodore 64, but its functionality is closer to the OPL(L|1|2|3)'s implementation of ADSR.
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- It features an 8-tap FIR filter, which is basically a procedural low-pass filter that you can edit however you want.
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- 7-bit volume, per-channel.
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- Per-channel 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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Note: this chip has a signed left/right level. Which can be used for inverted (surround) stereo. A signed 8-bit value means 80 - FF = -128 - -1. Other values work normally. A value of -128 is not recommended as it could cause overflows.
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- `10xx`: Set waveform.
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- `11xx`: Toggle noise generator mode.
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- `12xx`: Toggle echo on this channel.
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- `13xx`: Toggle pitch modulation.
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- `14xy`: Toggle inverting the left or right channels. (x: left, y: right)
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- `15xx`: Set envelope mode. (0: ADSR, 1: gain/direct, 2: decrement, 3: exponential, 4: increment, 5: bent)
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- `16xx`: Set gain. (00 to 7F if direct, 00 to 1F otherwise)
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- `18xx`: Enable echo buffer.
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- `19xx`: Set echo delay. (0 to F)
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- `1Axx`: Set left echo channel volume.
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- `1Bxx`: Set right echo channel volume.
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- `1Cxx`: Set echo feedback.
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- `1Dxx`: Set noise generator frequency. (00 to 1F)
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- `20xx`: Set attack (0 to F)
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- `21xx`: Set decay (0 to 7)
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- `22xx`: Set sustain (0 to 7)
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- `23xx`: Set release (00 to 1F)
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- `30xx`: Set echo filter coefficient 0
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- `31xx`: Set echo filter coefficient 1
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- `32xx`: Set echo filter coefficient 2
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- `33xx`: Set echo filter coefficient 3
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- `34xx`: Set echo filter coefficient 4
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- `35xx`: Set echo filter coefficient 5
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- `36xx`: Set echo filter coefficient 6
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- `37xx`: Set echo filter coefficient 7
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