[sdiy] Digital oscillators

[Scott Gravenhorst]

Tom Wiltshire <tom at electricdruid.net> wrote:
>
>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

Antti, I am also very interested in this.  I'm curious to see the code so that I
understand what you mean by "resource wasteful".  I'm mainly interested in using
FPGAs which can be resource rich to start with, so some "waste" to get something
good isn't really wasteful (c:

-- ScottG
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