16 bit sound

Posted on Feb 6, 2014

On several occasions, Acorn`s initial specifications for a new machine and the final product have differed considerably in the features they provide. For example, the Risc PC`s motherboard SCSI controller and Phoebe`s ultra-fast scratch memory were consigned to history before ever seeing the light of day. These were mainly as a result of cost-cutting measures on Acorn`s part when the

16 bit sound
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production cost of the final system was totted up. Another such casualty was the 16 bit sound system in the Risc PC, which was dropped on initial release to save a few pounds of parts. Acorn later realised that in the quantities they were dealing with, the cost of parts was tiny, so reintroduced this feature to motherboards that were shipped with RISC OS 3. 6 or 3. 7, but this left thousands of machines out there with the old system. Since the systems are different to access, software started to appear (such as PC Pro) that would not produce sound on the earlier machines. As the software to drive 16 bit sound is included in RISC OS 3. 6 or later, all that is required is the sound hardware. As the cost of parts is apparently so small, would it be possible to build a DIY 16 bit sound upgrade Commercial cards are available, so it must be possible, so I set out to find out. The 16 bit sound system in a Risc PC gives a sound output in digital format, which has to be fed to a DAC (Digital to Analogue Converter) to produce audio. Acorn`s costcutting measures meant this DAC and its associated clock were not present on early motherboards, so this is what we have to provide. The digital sound output arrives on the header LK8 directly from the VIDC chip in I ²S format. This is a standard devised by Philips for interconnecting digital audio components in CD players, DAT drives and so on. It is a serial output, where the 32 bits of...

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