Yamaha ADPCM

• Microsoft Audio ID: 0x0020
• Extension: spb,mmf
• Company: Yamaha
• Sample: http://samples.mplayerhq.hu/A-codecs/format-0x20-laugh.mmf
• ACM Codec: https://web.archive.org/web/20160323215457/http://smaf-yamaha.com/jp/tools/dl/Yamaha-ADPCM-ACM-Driver-100-j.zip

A variant of this codec is used by several Yamaha chips:

• Y8950(MSX-SOUND)
• YM2608（OPNA) [the external ADPCM channel only]

and may also be used on the following chips:

• YM2610(OPNB) [the external ADPCM_B channel only?]
• YMZ263B(MMA)
• YMZ280B(PCMD8)

A (possibly slightly changed) variant is used on the sound chip of Sega Dreamcast and NAOMI:

• Yamaha AICA Super Intelligent Sound Processor

The exact codec was also used by Yamaha SMAF MA-2 and onward):

• MA-2 (YMU759)
• MA-3 (YMU762)
• MA-5 (YMU765)
• MA-7 (YMU786)

The functionality of this codec is explained fairly extensively in two datasheets:

• Y8950 application manual: http://www.datasheetarchive.com/pdf/download.php?id=212962c2fe1b63fdc5ab320ca05ff3efefc925&type=M&query=y-8950
• YM2608 datasheet (Japanese): http://nemesis.hacking-cult.org/MegaDrive/Documentation/YM2608J.PDF
• Translated version of YM2608 datasheet: http://nemesis.hacking-cult.org/MegaDrive/Documentation/YM2608J%20Translated.PDF

The codec is almost a reference implementation of the codec described in Jayant's 1973 paper [1] (Table VIII, 'DPCM' column, B=4). This paper, along with its companion paper [2] originally coined the term "ADPCM".