SegaPCM

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SegaPCM

SegaPCM is the colloquial name of a PCM audio chip used by Sega in a number of arcade boards used by AM2 between 1985 and 1991. The chip's part number varies; see below. It was a custom ASIC manufactured by Sega. It was mainly used in the Super Scaler of high-end Sega arcade systems.

The chip is an 16-channel stereo digital mixing chip that uses external sample ROM. The chip is not pure stereo; it simply duplicates its input data on both left and right channels, allowing you to set the two channel volumes independnetly of each other to simulate panning. Samples play at a fixed frequency and can be looped. It presumably allows up to 16MB of sample ROM provided by the board but has additional banking hardware with a six bit bank number leading to a total of up to 1GB of addressable sample data (assuming optimal conditions). The sample format is some 8-bit PCM (what form it is is not yet determined by anyone here). Whether or not it produces an analog or digital signal is also undetermined by editors here. Samples must be aligned to some offset (TODO determine).

Rather than using this chip, Sega decided to use a simple DAC for its main arcade board at the time, the Sega System 16 board, for playing back samples, and continued to use a simple DAC in the System 24 before switching to chips by other vendors later.

Arcade boards with SegaPCM and part numbers

• Sega Hang-On hardware
  • All games: 315-5218
• Sega OutRun hardware
  • All games: 315-5218
• Sega X Board
  • All games: 315-5218 (unconfirmed)
• Sega Y Board
  • All games: 315-5218 (unconfirmed)

Technical specifications

The SegaPCM has the following technical specifications:

• Audio output: Stereo
• PCM audio channels: 16
• PCM audio bit depth: 12‑bit
• PCM sampling rate: 31.25 kHz

Sega MultiPCM

The SegaPCM was succeeded by the Sega MultiPCM, a more advanced PCM sound chip that was later used in the Sega System Multi 32, Sega Model 1 and Sega Model 2 arcade boards. It is based on the Yamaha YMF278 sound chip.

The Sega MultiPCM has the following technical specifications:

• Part number: 315-5560
• Audio output: Stereo
• PCM audio channels: 28
• PCM audio bit depth: 16‑bit
• PCM sampling rate: 44.1 kHz (CD quality)