[sdiy] Digital oscillators

[Tom Wiltshire]

On 29 Dec 2008, at 14:47, Antti Huovilainen wrote:

> On Sun, 28 Dec 2008, Tom Wiltshire wrote:
>
>> I don't exactly how good the technique is supposed to be, but I'd  
>> be bloody astounded if it could generate an alias-free square wave  
>> at half the sample rate.
>
> Getting right up to nyquist is somewhat tricky, but say 0.95x  
> nyquist is no problem (wasteful for resources but in no way  
> difficult). With BLEP the problem is reduced to FIR filter design.

0.95x nyquist? Impressed!

>> To be honest, I''d be impressed if you could generate a noise-free  
>> *sine* wave at that frequency without heavy filtering afterwards.  
>> I know (from bitter experience!) that it isn't as easy as I  
>> thought it would be, even with a 60+KHz sample rate and a 2048- 
>> entry wavetable.
>
> You did use interpolation I hope?
> With linear interp, you shouldn't need larger than 64..256 entry  
> lookup table.

No, I didn't have time. Hence the use of such a large table. The  
heavy oversampling was an attempt to reduce errors another way.

> I'll try to get around to posting simple example code for alias  
> free sawtooth synthesis with BLEP once I get back from holidays.

Your stuff is always interesting, Antti.

Tom