Andrew J wrote:Hi all,
As hinted elsewhere on the forum, I've been working on a toolkit for oversampling - and now it's ready! So take a look at the wiki tutorial (which is inside the DSP section of the tutorials). You'll find a schematic containing the ASM-optimised filters towards the bottom of the page, there's also an example schematic to play with.
Thanks to sambean for originally providing the code for the polyphase IIR filter, and to aliasant for user testing and feedback.
Please post any comments/issues here.
MyCo wrote:Hi Andrew!
This is exactly what I described in the other thread, which you are refering to. But your explanation is totaly missleading, and I don't think there are many people outside that realy understand how simple it is. The way you describe it is just to difficult. The basic idea is just: calculate an imaginary sample between 2 real samples, the easiest way is a moving average filter which is the most simple lowpass filter. Then process the real-stream and the imaginary-stream you describe it as "oversampling process" and at the end you just mix the to streams together with another lowpass filter (the moving average filter could do this too).
My english is too bad, to explain it in "Fachchinesisch" (technical mumbo-jumbo [???])
And for me, it is still a fake oversampling, because it isn't processed at higher sample rate. The right term for this in my opinion is "double processing"
exonerate wrote:It seems that in your example schematic the triangular and power oversampling requires a gain boost by the oversampling factor to be at the same volume level as the polyphase. I guess thats to do with the quality of the filters and the roll off?
MyCo wrote:In "true" oversampling, you can generate waveforms with let's say FS/2 which have 4 samples so you can see what it is:
sine: 0 1 0 -1
saw: -1 -0.3 0.4 1
ramp: 1 0.4 -0.3 -1
pulse: -1 -1 1 1
in "fake" oversampling FS/2 is a pulse (-1 1) and it depends on the filter how it looks like oversampled. But you can NEVER generate different waveforms at this frequency.
And this is not what you are looking for, if you need oversampling...
bootsy wrote:great stuff - thanks for sharing and thanks especially for the detailed comments in the ASM
watch out for denormals when using the polyphase filter.
MyCo wrote:And for me, it is still a fake oversampling, because it isn't processed at higher sample rate. The right term for this in my opinion is "double processing"
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