[sdiy] PIC-based Digital Oscillator question

[dan snazelle]

On Apr 23, 2011, at 6:20 PM, Tom Wiltshire wrote:

> 
> On 23 Apr 2011, at 22:55, Ian Smith wrote:
> 
>> 
>> 
>>> Hi Ian,
>>> 
>>> Have a look at the VCLFO code on my website:
>>> 
>>> http://www.electricdruid.net/index.php?page=projects.lfo9
>>> 
>>> It's a phase accumulator based oscillator, in this case at low frequencies not audio, but the principles the same.
>>> There's a quirk in that I implemented simple phase distortion ("waveform distortion") so it uses different frequency increments for the first half of the waveform and the second half, but you can ignore that.
>>> 
>>> HTH,
>>> Tom
>> 
>> Let me see if I am understanding this correctly: For the phase accumulator and the frequency increment, every time you overflow the phase accumulator, the frequency increment is incremented by one and the top how-many-ever bits of the frequency increment are used to look up a value from the waveform table. So the faster you increment through the phase accumulator, the higher the frequency of the output.
>> -Ian
> 
> Nearly. There's no need to alter the frequency increment. 
> 
> Every sample you add the frequency increment to the phase accumulator, and then you use the top how-ever-many bits for the lookup, like you said. The larger the frequency increment, the faster the phase accumulator will overflow and the higher the frequency of the output.
> 
> There's a page on my site explaining the principles if you're interested:
> 
> http://www.electricdruid.net/index.php?page=info.dds
> 
> Tom.
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> 
IS DDS the same as wavetable?

I didn't start hearing DDS until recently when I started using the Arduino and looking for ways to make oscillators.

thanks!


great page btw