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204 lines
12 KiB
Markdown
204 lines
12 KiB
Markdown
# 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 Sony-developed audio system features a DSP chip, SPC700 CPU, and 64KB of dedicated SRAM used by both.
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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:
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- pitch modulation.
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- a built in noise generator, useful for hi-hats, cymbals, rides, effects, among other things.
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- per-channel echo, which unfortunately eats up a lot of memory but can be used to save channels in songs.
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- an 8-tap FIR filter for the echo, which is basically a procedural low-pass filter that you can edit however you want.
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- sample loop, but the loop points have to be multiples of 16.
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- left/right channel invert for surround sound.
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- ADSR and gain envelope modes.
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- 7-bit volume per channel.
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- 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.
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## effects
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- `10xx`: **set waveform.**
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- `11xx`: **toggle noise mode.**
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- `12xx`: **toggle echo on this channel.**
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- `13xx`: **toggle pitch modulation.** frequency modulation by the previous channel's output. no effect on channel 1.
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- `14xy`: **toggle inverting the left or right channels.** `x` is left, `y` is right.
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- `15xx`: **set envelope mode.** see gain chart below for `1` through `5`.
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- `0`: ADSR mode.
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- `1`: gain (direct). volume holds at one level.
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- `2`: linear decrement. volume lowers by subtractions of 1/64.
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- `3`: exponential decrement. volume lowers by multiplications of 255/256.
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- `4`: linear increment. volume rises by additions of 1/64.
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- `5`: bent line (inverse log) increment. volume rises by additions of 1/64 until 3/4, then additions of 1/256.
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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.** range is `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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- all of these are signed numbers.
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- `00` to `7F` for 0 to 127.
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- `80` to `FF` for -128 to -1.
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- setting these to -128 is not recommended as it may cause echo output to overflow and therefore click.
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- `1Dxx`: **set noise generator frequency.** range is `00` to `1F`. see noise frequencies chart below.
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- `1Exx`: **set left dry / global volume.**
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- `1Fxx`: **set right dry / global volume.**
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- these do not affect echo.
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- `20xx`: **set attack.** range is `0` to `F`.
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- `21xx`: **set decay.** range is `0` to `7`.
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- `22xx`: **set sustain.** range is `0` to `7`.
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- `23xx`: **set release.** range is `00` to `1F`.
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- these four are only used in ADSR envelope mode. see ADSR chart below.
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- `3xyy`: **set echo filter coefficient.**
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- `x` is the coefficient from 0 to 7.
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- `yy` is the value (signed number).
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- `00` to `7F` for 0 to 127.
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- `80` to `FF` for -128 to -1.
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- note: be sure the sum of all coefficients is between -128 and 127. sums outside that may result in overflow and therefore clicking.
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- see SnesLab for [echo filter explanations and examples](https://sneslab.net/wiki/FIR_Filter#Uses).
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## info
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this chip uses the [SNES](../4-instrument/snes.md) instrument editor.
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when two channels are joined for pitch modulation, the channel bar will show `mod` on a bracket tying them together.
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when using sample offset commands, be sure to open each involved sample in the sample editor, look to the "Info" section at the top-left, and check the "no BRR filters" box. this prevents sound glitches, at the cost of lowering the sample quality to 4-bit.
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## channel status
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the following icons are displayed when channel status is enabled in the pattern view:
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- envelope/gain status:
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-  direct gain
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-  linear gain decrease
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-  logarithmic gain decrease
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-  linear gain increase
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-  bent-line gain increase
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-  envelope attack
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-  envelope decay
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-  envelope sustain
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-  envelope release
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## chip config
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the following options are available in the Chip Manager window:
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- **Volume scale**: scale volumes to prevent clipping/distortion.
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- **Enable echo**: enables the echo buffer.
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- **Initial echo state**: selects which channels will have echo applied.
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- **Delay**: sets echo length.
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- **Feedback**: sets how much of the echo output will be fed back into the buffer.
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- **Echo volume**: sets echo volume.
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- **Echo filter**: adjusts echo filter.
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- **Dec/Hex**: toggles decimal or hexadecimal mode for the filter settings text entry box to the right.
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- SnesLab provides [echo filter explanations and examples](https://sneslab.net/wiki/FIR_Filter#Uses). their example filter strings can be pasted directly into the filter settings text entry box if set to Hex mode.
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## ADSR
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| attack | 0→1 time | decay | 1→S time | sustain | ratio | release | S→0 time
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| -----: | -------: | ----: | -------: | ------: | :---: | ------: | -------:
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| `00` | 4.1s | `00` | 1.2s | `00` | 1/8 | `00` | ∞
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| `01` | 2.5s | `01` | 740ms | `01` | 2/8 | `01` | 38s
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| `02` | 1.5s | `02` | 440ms | `02` | 3/8 | `02` | 28s
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| `03` | 1.0s | `03` | 290ms | `03` | 4/8 | `03` | 24s
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| `04` | 640ms | `04` | 180ms | `04` | 5/8 | `04` | 19s
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| `05` | 380ms | `05` | 110ms | `05` | 6/8 | `05` | 14s
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| `06` | 260ms | `06` | 74ms | `06` | 7/8 | `06` | 12s
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| `07` | 160ms | `07` | 37ms | `07` | 1 | `07` | 9.4s
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| `08` | 96ms | | | | | `08` | 7.1s
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| `09` | 64ms | | | | | `09` | 5.9s
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| `0A` | 40ms | | | | | `0A` | 4.7s
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| `0B` | 24ms | | | | | `0B` | 3.5s
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| `0C` | 16ms | | | | | `0C` | 2.9s
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| `0D` | 10ms | | | | | `0D` | 2.4s
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| `0E` | 6ms | | | | | `0E` | 1.8s
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| `0F` | 0ms | | | | | `0F` | 1.5s
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| | | | | | | `10` | 1.2s
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| | | | | | | `11` | 880ms
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| | | | | | | `12` | 740ms
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| | | | | | | `13` | 590ms
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| | | | | | | `14` | 440ms
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| | | | | | | `15` | 370ms
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| | | | | | | `16` | 290ms
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| | | | | | | `17` | 220ms
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| | | | | | | `18` | 180ms
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| | | | | | | `19` | 150ms
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| | | | | | | `1A` | 110ms
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| | | | | | | `1B` | 92ms
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| | | | | | | `1C` | 74ms
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| | | | | | | `1D` | 55ms
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| | | | | | | `1E` | 37ms
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| | | | | | | `1F` | 18ms
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reference: [Super Famicom Development Wiki](https://wiki.superfamicom.org/spc700-reference#dsp-voice-register:-adsr-1097)
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## gain
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value | linear inc. | bent line inc. | linear dec. | exponent dec.
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----: | ----------: | -------------: | ----------: | ------------:
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`00` | ∞ | ∞ | ∞ | ∞
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`01` | 4.1s | 7.2s | 4.1s | 38s
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`02` | 3.1s | 5.4s | 3.1s | 28s
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`03` | 2.6s | 4.6s | 2.6s | 24s
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`04` | 2.0s | 3.5s | 2.0s | 19s
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`05` | 1.5s | 2.6s | 1.5s | 14s
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`06` | 1.3s | 2.3s | 1.3s | 12s
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`07` | 1.0s | 1.8s | 1.0s | 9.4s
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`08` | 770ms | 1.3s | 770ms | 7.1s
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`09` | 640ms | 1.1s | 640ms | 5.9s
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`0A` | 510ms | 900ms | 510ms | 4.7s
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`0B` | 380ms | 670ms | 380ms | 3.5s
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`0C` | 320ms | 560ms | 320ms | 2.9s
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`0D` | 260ms | 450ms | 260ms | 2.4s
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`0E` | 190ms | 340ms | 190ms | 1.8s
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`0F` | 160ms | 280ms | 160ms | 1.5s
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`10` | 130ms | 220ms | 130ms | 1.2s
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`11` | 96ms | 170ms | 96ms | 880ms
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`12` | 80ms | 140ms | 80ms | 740ms
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`13` | 64ms | 110ms | 64ms | 590ms
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`14` | 48ms | 84ms | 48ms | 440ms
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`15` | 40ms | 70ms | 40ms | 370ms
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`16` | 32ms | 56ms | 32ms | 290ms
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`17` | 24ms | 42ms | 24ms | 220ms
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`18` | 20ms | 35ms | 20ms | 180ms
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`19` | 16ms | 28ms | 16ms | 150ms
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`1A` | 12ms | 21ms | 12ms | 110ms
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`1B` | 10ms | 18ms | 10ms | 92ms
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`1C` | 8ms | 14ms | 8ms | 74ms
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`1D` | 6ms | 11ms | 6ms | 55ms
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`1E` | 4ms | 7ms | 4ms | 37ms
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`1F` | 2ms | 3.5ms | 2ms | 18ms
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reference: [Super Famicom Development Wiki](https://wiki.superfamicom.org/spc700-reference#dsp-voice-register:-gain-1156)
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## noise frequencies
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value | freq. | value | freq.
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----: | -----: | ----: | -------:
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`00` | 0 Hz | `10` | 500 Hz
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`01` | 16 Hz | `11` | 667 Hz
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`02` | 21 Hz | `12` | 800 Hz
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`03` | 25 Hz | `13` | 1.0 KHz
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`04` | 31 Hz | `14` | 1.3 KHz
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`05` | 42 Hz | `15` | 1.6 KHz
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`06` | 50 Hz | `16` | 2.0 KHz
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`07` | 63 Hz | `17` | 2.7 KHz
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`08` | 83 Hz | `18` | 3.2 KHz
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`09` | 100 Hz | `19` | 4.0 KHz
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`0A` | 125 Hz | `1A` | 5.3 KHz
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`0B` | 167 Hz | `1B` | 6.4 KHz
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`0C` | 200 Hz | `1C` | 8.0 KHz
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`0D` | 250 Hz | `1D` | 10.7 KHz
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`0E` | 333 Hz | `1E` | 16 KHz
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`0F` | 400 Hz | `1F` | 32 KHz
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reference: [Super Famicom Development Wiki](https://wiki.superfamicom.org/spc700-reference#dsp-register:-flg-1318)
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## resources
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- [SNES-format BRR samples](https://www.smwcentral.net/?p=stion&s=brrsamples) at SMW Central
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