[sdiy] Digital oscillators [was: Active VCO temp compensation]

[Simon Brouwer]

Tom Wiltshire schreef:
>
> On 23 Dec 2008, at 22:30, Seb Francis wrote:
>
>> Antti Huovilainen wrote:
>>>
>>> 5b) BandLimited StEps (BLEP)
>>> For each oscillator reset, sum a bandlimited step with the trivial
>>> saw. The steps are precalculated and stored in a table (can be
>>> quite short when interpolation is used between two phases.
>>>
>>> Pros: Very good quality. No oversampling required. Can do
>>> bandlimited FM, PWM and sync. Probably the only method that can do
>>> audio rate PWM and sync.
>>> Cons: Requires a divide per cycle. Can be complicated: calculating
>>> required table entry is not trivial when using sync or pwm.
>>>
>>
>> For anyone trying to get their head around this (like me!), here's
>> an easily-understandable introduction...
>> http://www.slack.net/~ant/bl-synth/
>>
>> Seb
>
> This is a very clear walkthrough of the technique. One thing I did
> notice, though, is that on section 11 (http://www.slack.net/~ant/bl-
> synth/11.implementation.html) where they talk about storing different
> versions of the bandlimited step according to the subsample offset,
> what they're really talking about is oversampling the waveform.
> E.g. It'd probably be neater to just store one heavily oversampled
> bandlimited step, rather than have a whole array of separate tables
> for different subsample offsets like they suggest. It amounts to the
> same thing, anyway.

It may be more efficient to use separate tables, as you can increment the
index by 1 instead of skipping n-1 entries when filling the buffer of
differences.

-- 
Vriendelijke groet,

Simon Brouwer
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