[sdiy] Top Octave Generator (was Chinese MG-1s??!?)

[Tom Wiltshire]

On 2 May 2008, at 00:10, Eric Brombaugh wrote:

> Tom Wiltshire wrote:
>
>> The best way to replace a TOG with PICs would be to use little 8- 
>> pin chips and use twelve of them!
>> If that seems like too many chips, pull all the divider chips out  
>> as well, and then replace the TOG and the dividers by having  
>> twelve chips that each produce a single note at all required octaves.
>
> Don't you think you could get 12 square-wave NCOs into a single  
> dsPIC33F running at the full 40MHz clock rate? It might be a little  
> tight, but I bet you could do it. You might sacrifice a little  
> frequency resolution by running them on only 16-bit phase  
> accumulators to speed things up a tad, but it probably wouldn't be  
> any worse than the 9-bit divisors mentioned earlier.

Yes, I'm sure you could on a dsPIC, but I wanted a 8-bit solution!  
(Ok, I know I'm just being too demanding...)

Actually, my motivation for saying the 'best way' was to use twelve  
chips was just that it regains the free-phase element between the  
notes of the octave. As Paul Perry pointed out, this makes a big  
difference to the sound. Obviously it'd be neater (and more  
satisfying from an engineering point of view!) to get it all onto one  
chip.

Byron's idea of finding something that has 12 PWM modules and then  
using those to produce the output frequencies is good, and that might  
even work on 8-bit chips. You might need a couple of them I suppose,  
but still.

One other idea that occurs is whether there might be a way to do this  
with vertical counters. They tend to be very efficient codewise (and  
therefore quick). Perhaps that's how the NCOs could be done.

T.