54 lines
2.5 KiB
Markdown
54 lines
2.5 KiB
Markdown
# Atari Lynx instrument editor
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Atari Lynx instrument editor consists of two tabs: Sample and Macros.
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## Sample
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for sample settings, see [the Sample instrument editor](sample.md).
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the only differences are the lack of an "Use wavetable" option, and the presence of a "Use sample" one.
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note that using samples on Lynx is CPU expensive!
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## Macros
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- **Volume**: volume sequence.
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- **Arpeggio**: pitch sequence.
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- **Duty/Int**: bit pattern for LFSR taps and integration.
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- **Panning (left)**: output level for left channel.
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- **Panning (right)**: output level for right channel.
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- **Pitch**: fine pitch.
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- **Phase Reset**: trigger restart of waveform/LFSR reset.
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- **Load LFSR**: load a value to the LFSR.
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## audio generation description
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Atari Lynx generates sound using a 12-bit linear feedback shift register (LFSR) with configurable tap. nine separate bits can be enabled to be the source of feedback: 0, 1, 2, 3, 4, 5, 7, 10 and 11. to generate _any_ sound at least one bit _must_ be enabled.
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### LFSR-based synthesis
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a linear-feedback shift register is one method used for random number generation.
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it works by shifting a sequence of binary numbers (bits), taking the last bit into the output. then some of the bits are combined with others, doing a XOR (exclusive or) operation and then being pushed back.
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think of it as a conveyor carrying glass bottles. each bottle may be empty or carrying water.
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the bottle at the end is taken. if there's water, then the output is 1. if it's empty, the output is 0.
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depending on the LFSR configuration, many bottles at specific positions ("taps") are looked at. these are combined from left to right, two by two:
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- if two bottles are identical, an empty bottle is pushed.
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- if one bottle has water but the other is empty, a water bottle is pushed.
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the process is repeated indefinitely.
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unlike PowerNoise, Lynx's taps are in fixed positions, but it has many of them.
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### square wave
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the LFSR is shifted at the rate define by sound pitch and generates square wave by setting channel output value to +volume or -volume, depending on the bit shifted in.
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### triangle wave
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alternatively when "int" bit is set sound wave is generated by adding or subtracting volume from output effectively producing triangle wave.
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#### how triangle wave works?
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hint: to obtain triangle set bits "int" and "11" in "Duty/Int" sequence and set volume to about 22.
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by enabling 11th tap bit the value shifted in is negated after 11 bit is shifted in hence the volume is added for 11 cycles and then subtracted for 11 cycles.
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