[sdiy] Korg DSS1 DMA oscillators, the old beast!

[Tom Wiltshire]

On 23 Jan 2010, at 00:00, karl dalen wrote:

> http://img14.imageshack.us/img14/6212/dss3.jpg
> http://img691.imageshack.us/img691/7066/dss2.jpg
> http://img715.imageshack.us/img715/3315/dss1.jpg
>
> It appears that DSS1 are a true variable sample rate system with
> crude Bw limiting in Wave Draw and Additive modes but not in sample  
> mode
> according to T0 to T15 producing the musical note (variable sample  
> rate)  but how does this DMA actually work as variable playback  
> mechanism to
> generate the actual sample tone?

It looks like it uses the 32MHz clock and 19-bit divider to generate  
the sample rate. This presumably generates DMA signals/interrupts.  
When a interrupt arrives, the DMA transfers a sample from the DRAM to  
the DAC. The purpose of DMA is really to move data about *without  
involving the CPU* - speed benefits are a consequence of this. In  
this case, that's probably because the poor CPU(s) have got quite  
enough to do already.

> Noise in the DSS1 are generated completely analog by something
> old fashioned as blurbing PN junctions! :)

I'm not surprised. Korg put an MM5837 digital noise source in the  
Monopoly, and then had to change it for an analog source in later  
versions. Once burned, twice shy.

Regards,
Tom