Difference between revisions of "Saturn Custom Sound Processor"

Latest revision as of 14:18, 10 August 2024

Saturn Custom Sound Processor

Designer: Yamaha

The Yamaha YMF292, also known as the Saturn Custom Sound Processor (abbreviated as SCSP) is a sound chip created by Yamaha for the Sega Saturn, before also making its way into the Sega Model 2A-CRX, Model 2B-CRX, and Sega Model 3 arcade boards.

Hardware

The SCSP contains 32 channels of sample-based audio. In addition to playing back samples with a variety of different loop settings, each SCSP channel can further shape the sound of its samples using ADSR envelopes and an LFO generator (used for hardware vibrato or tremolo effects), and can send its output audio directly to the speakers and to one of the 16 input slots on the chip's Digital Signal Processor (DSP). The DSP itself is a programmable effects unit that can perform up to 128 microcode operations on its input slots to create delay, filtering, and many other audio effects.

One rarely-used feature unique to the SCSP is its FM functionality, which allows any channel to have its sample data be modulated by the stored audio output of up to two other channels (including itself). Because of the freeform nature of this operation, there is no limit to how the SCSP's channels can be arranged—one song can use all 32 of its channels for direct PCM playback, another song can split its channels into 16 2-OP PCM/FM instruments, while another still could use 3 5-OP instruments, 4 3-OP instruments, and 7 direct playback channels. Additionally, songs that use the DSP may reserve some channels for effects inputs (like an LFO for a chorus effect) instead of as playback channels or modulators.

The Sega Saturn's audio RAM is connected directly to the SCSP, and is used to store the samples, sound programs (e.g. Cybersound), and any other data needed by the music and sound effects. The entire chip is controlled by a single Motorola 68EC000 16-bit CPU running at 11.3Mhz, which is essentially the same as (and compatible with) the M68000 used in the Mega Drive and several other consoles, but without the 8-bit MC6800 interface. The SCSP can also be directly accessed by both SH-2s in the Saturn, although it was more common to leave as much of the sound processing to the 68EC000 as possible.

The SCSP only operates on raw 8-bit or 16-bit big-endian PCM data, with no native support for compressed samples. Many later Sega Saturn games, however, would store longer sound effects or music as compressed ADX data, which would be decompressed and played by the 68EC000 in real time. Although the SCSP supported MIDI inputs through the Saturn MIDI Interface Box, the only games to take advantage of this feature were Saturn Music School and its sequel.

Technical information

44.1 kHz sampling rate (CD quality)
22.6 MHz Yamaha FH1 digital signal processor
All 32 slots can be used for PCM sample playback
Any of 32 slots can be linked together for multiple operators per FM sound channel

Documentation

User's Manual (ST-077-R2-052594)

References

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 ==Hardware==
-The SCSP is a multi-function game sound generator LSI that consists of a PCM sound generator and a DAC (Digital Audio Converter). The SCSP creates and processes sound mixes. It contains a 32 slot sound generator and sound effect DSP, 16 channel digital mixer and timer, and an interrupt controller. The Saturn's audio RAM is connected directly to the SCSP, and is used to store the sound programs (i.e. [[Cybersound]]) or raw waveform samples. The SCSP can support up to 32 channels for PCM sample playback, or 32 operators for FM synthesis (up to 32 channels of 1-op FM, 16 channels of 2-op FM, 8 channels of 4-op FM, or 5 channels of 6-op FM). Maximum sample rate for PCM samples is 44.1Khz. The SCSP is [[MIDI]]-compliant, and can be hooked up to external equipment (such as keyboards).
+The SCSP contains 32 channels of sample-based audio. In addition to playing back samples with a variety of different loop settings, each SCSP channel can further shape the sound of its samples using ADSR envelopes and an LFO generator (used for hardware vibrato or tremolo effects), and can send its output audio directly to the speakers and to one of the 16 input slots on the chip's Digital Signal Processor (DSP). The DSP itself is a programmable effects unit that can perform up to 128 microcode operations on its input slots to create delay, filtering, and many other audio effects.
-The 128 step Digital Signal Processor is capable of generating special effects such as reverberation and different room acoustics.
+One rarely-used feature unique to the SCSP is its FM functionality, which allows any channel to have its sample data be modulated by the stored audio output of up to two other channels (including itself). Because of the freeform nature of this operation, there is no limit to how the SCSP's channels can be arranged—one song can use all 32 of its channels for direct PCM playback, another song can split its channels into 16 2-OP PCM/FM instruments, while another still could use 3 5-OP instruments, 4 3-OP instruments, and 7 direct playback channels. Additionally, songs that use the DSP may reserve some channels for effects inputs (like an LFO for a chorus effect) instead of as playback channels or modulators.
-On the Saturn, the entire SCSP is controlled by a single Motorola 68EC000 16-bit CPU running at 11.3Mhz. The MC68EC000 is essentially the same as (and compatible with) the M68000 used in the Mega Drive and several other consoles, but without the 8-bit MC6800 interface. The SCSP can be directly accessed by the MC68EC000 and both [[Hitachi SuperH2 7604 32-Bit RISC|SH-2s]].
+The Sega Saturn's audio RAM is connected directly to the SCSP, and is used to store the samples, sound programs (e.g. [[Cybersound]]), and any other data needed by the music and sound effects. The entire chip is controlled by a single Motorola 68EC000 16-bit CPU running at 11.3Mhz, which is essentially the same as (and compatible with) the M68000 used in the Mega Drive and several other consoles, but without the 8-bit MC6800 interface. The SCSP can also be directly accessed by both [[Hitachi SuperH2 7604 32-Bit RISC|SH-2s]] in the Saturn, although it was more common to leave as much of the sound processing to the 68EC000 as possible.
-The SCSP is a capable system limited only by the small amount of RAM made available to it, and a lack of built-in hardware sample compression.
+The SCSP only operates on raw 8-bit or 16-bit big-endian PCM data, with no native support for compressed samples. Many later Sega Saturn games, however, would store longer sound effects or music as compressed [[ADX]] data, which would be decompressed and played by the 68EC000 in real time. Although the SCSP supported MIDI inputs through the [[Saturn MIDI Interface Box]], the only games to take advantage of this feature were [[Saturn Music School]] and its [[Saturn Music School 2|sequel]].
 ==Technical information==
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 * All 32 slots can be used for PCM sample playback
 * Any of 32 slots can be linked together for multiple operators per FM sound channel
-* Usually four operators used per slot for 8 FM channels total
 ==Documentation==