Having two different DMA channels allows for full-duplex, ie. simultaneous playback and recording, necessary eg. for Internet telephony.

Good to know. Any other implications?

maxtherabbit wrote on 2020-03-18, 02:44:

16bit audio works just fine when it's set to "use low DMA" so why bother using up additional resources? Is there any advantage to having a high DMA channel defined on a SB16?

Using the low DMA for 16-bit audio is more complicated, as DMA 0-3 are 8-bit wide, so 16-bit data can only be transfered in chunks of 8 bits. Also, lots of games simply don't support it.

Having two different DMA channels allows for full-duplex, ie. simultaneous playback and recording, necessary eg. for Internet telephony.

Full-duplex refers to the fact that the same quality can be used in both ways at the same time (playback + recording), whereas half-duplex sacrifices quality for recording. This has nothing to do with having two DMA channels. There are 16-bit cards that can't do full-duplex, as that is simply a feature the codec either has or not.

derSammler wrote on 2020-03-18, 06:59:

...
Full-duplex refers to the fact that the same quality can be used in both ways at the same time (playback + recording), whereas half-duplex sacrifices quality for recording. This has nothing to do with having two DMA channels...

Are you sure? I do not know the implementation details of SB16 but e.g. ESS 1869 uses 2 low DMA channels and the only purpose of the 2nd DMA is to achieve full duplex operation.
https://www.diamondsystems.com/files/binaries … 9techmanual.pdf

The ES1869 Audio Drive® solution can record, compress, and play back voice, sound, and music with built-in mixer controls. […]
Show full quote

The ES1869 Audio Drive®
solution can record, compress,
and play back voice, sound, and music with built-in mixer
controls. It supports full-duplex operation for simultaneous
record and playback using two DMA channels.

Also from Wikipedia:
https://en.wikipedia.org/wiki/Sound_card

Feature evolution
Early ISA bus sound cards were half-duplex, meaning they couldn't record and play digitized sound simultaneously, mostly due to inferior card hardware (e.g., DSPs). Later, ISA cards like the SoundBlaster AWE series and Plug-and-play Soundblaster clones eventually became full-duplex and supported simultaneous recording and playback, but at the expense of using up two IRQ and DMA channels instead of one, making them no different from having two half-duplex sound cards in terms of configuration. Towards the end of the ISA bus' life, ISA sound cards started taking advantage of IRQ sharing, thus reducing the IRQs needed to one, but still needed two DMA channels.

High DMA channels let you transfer 16bits in one cycle rather than two. That is pretty much the only reason these channels exist and why they are used. WSS cards only use 8bit DMA channels and do twice as many DMA cycles compared if they used 16bit DMA that SB16 and few others can do.

Some motherboards are buggy when using High DMA, mostly older <1997. You can test this with creative's diagnose.exe program, if it still hangs testing hight DMA when everything is configured properly with no IRQ conflicts.
The only benefit is less overhead. Game music in later Dos games will still play back using 16bit sound only using low DMA but theoretically with more overhead. Probably more noticeable on a 386.
Only problem is some game setup/config programs won't work unless you select a high dma. You get around this by using the same low dma # for the high DMA(or edit the setup file). Also use set blaster with the same low dma as high i.e =A220 I7 D1 H1.