On 02/01/2011 10:34, MCH wrote:
> Any Assembly code examples you could point me to? How much resolution
> would I need? 8-bit? 16-bit? More? I want a pretty pure sounding since
> wave. I know the more the better, but certainly there is a point that is
> nearing a true sine wave for practical audio purposes.
6bits is usable but noisy & distorted
8bits is what ISDN uses (with uLaw or Alaw compression)
16bits is what CDs use.

The sample rate and bit resolution depend on post filtering and amount=20
of distortion you want
"pretty pure sounding" can be done with 1 bit on/off at desired=20
frequency and suitable filter. So you need to define how pure sounding,=20
frequency and amplitude range and amount of analogue filtering to be used.

Usually I use a 1/4 table of sine values (calculated in a spreadsheet=20
using scaled fixed point arithmetic for result where 1 =3D max int)  at=20
8bit or 16 bit resolution for output to PWM register or DAC. you change=20
the DAC or PWM register at the audio sample rate. The PWM clock=20
frequency will be a minimum of PWM bits x sample rate. Sample rate is a=20
minimum of twice your highest audio frequency. Oversampling (x4, x8, x16=20
etc) allows for simpler single R C filter  for desired distortion level.

So pick highest speed your PWM / PIC can go at.


--=20
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