[sdiy] Wavetable Design Update

[Dave Manley]

On 2/5/2011 12:44 PM, ASSI wrote:
> On Saturday 05 February 2011, Dave Manley wrote:
>> Here's some output from the spread sheet I did the other day:
>>
>> Midi    Counter Freq            Note Freq       20 MHz  Note Freq
>
> You're off by a factor of two (or a whole octave), the effective frequency
> is 10MHz in CTC mode since the output is toggled with the timer overflow -
> producing a divide by two.  It may be possible to work around this
> particular limitation by using one of the PWM modes at the expense of a very
> narrow clock pulse, I don't know the timer good enough to be sure.  This
> sort of oscillator works best with a VCO doing the clock generation or with
> a much higher input frequency.  You don't really need GHz clocks if you use
> a fractional divider.

I don't know the capabilities of the micro in question.  I guess there's
at least three options to not run at half rate:

1. route the overflow pulse to an output
2. interrupt on overflow and pulse an output (not possible at high freq)
3. the CPLD generates a pulse based on 1/2 rate edges from the micro

So what about running the wavetables with reduced depth?  How
bad would it sound and what's the easy way to generate some
audio files to try it?

-Dave