[sdiy] Single chip digital delay

[Seb Francis]

Hi Anthony,

anthony wrote:

> I just thought I'd pipe in to add: why do you think a single-chip 
> delay would be much better than a BBD? Maybe a little edge in S/N. If 
> you used an MN3005 and clocked it fast you'd get a short delay. I use 
> an MN3006 (128 stage - shorty) with a double-notch filter. I clock it 
> at about 200 kHz. I also use R5106's (512 stage). I think these sound 
> very good, but the actual S/N is lower.
>  

You might be right that a single chip delay would not be much better 
than a BBD.  In which case, it will not be good enough for me.  For my 
purposes I definitely need a clean (get out what you put in) delay of 5 
to 50ms.  CD (44.1kHz/16bit) is the kind of quality level I'm aiming for.

Actually I'm now moving slightly away from the idea of a single chip 
delay as I don't think the quality will be good enough.  I was hoping to 
get some samples of the Mitsubishi (now Renesas) M65830 to try, but they 
turned down my samples request.  Anyway, from the datasheet the quality 
didn't really look good enough.

One key thing I'd like to achieve is consistent quality with different 
delay times.  So ideally I'd like to vary the buffer size not the clock 
rate.

But I still do want a simple (minimum component count) solution...

My current thinking is to use a high end PIC with some kind of ADC and 
DAC on the front and back of it.  Yes I know a DSP chip would be better, 
but I have a PIC programmer and I know how to program PICs.  As for the 
ADC and DAC, I haven't decided whether to use hand-rolled adaptive Delta 
modulator converters at ~750kHz/1bit, or just to use off the shelf 
converters at 48kHz/16bit.  As for RAM, I was planning to use the 
internal RAM of the PIC, but this would only be enough for 1 channel (I 
want 2 independent delays), so rather than add a second PIC for the 2nd 
channel I may as well just add an external RAM chip.

> Now if they make a single-chip delay that does 192 kHz/32-bit well 
> then I'm there...
>  
> I bought a Soundblaster at Wal-Mart not looking closely at the box - 
> seeing only 192 kHz. That was just tej stinking digital playback. 
> Rats. But I'm getting OT. Not to mention the cheap soundblasters sound 
> absolutely HORRIBLE on XP. I wish I'd saved the money I spent on a new 
> Dell and got a used G4 Mac.

Well, I don't want to get into the whole PC vs Mac debate, but my PC 
sounds spot on .. then again I do have a proper studio soundcard.  In 
any case if you want to use any kind of music software you're going to 
want decent ASIO drivers (not the crap that comes from Creative).  The 
EMU sound cards are a good bet if you don't want to spend too much.

Seb