Resampler Quality


#1

I was under the impression that the Juce resampler is top-notch, but while messing with the ffmpeg resampler, I came across this site: http://src.infinitewave.ca

The Juce resampler seems like one of the less good options?

Jules - any comment on this? I’d rather stick with working Juce code, but would you recommend ffmpeg (or ffmpeg/sox) over it if I’m using their resampler anyway (do do channel layout work).

Bruce


#2

It’s not clear whether they’re using the ResamplingAudioSource (which uses a very simple low-pass filter and linear interpolation - i.e. quick-and-dirty) or the LagrangeInterpolator (which is mainly useful for dynamically varying pitches). Neither one was ever designed to be a really high quality fixed-ratio algorithm, which is what they’re testing for. I’m not much of an expert on resampling myself, but if anyone can point me at a free, simple algorithm that’d be a good addition to the library, I’d be interested!


#3

Basically the best (really the best, there is no better!!) affordable re-sampling is to map a sinc-funcition (which needs to be bandlimited (pitched) when the destination sample-rate is lower than source-samplerate) on every source sample-point, and then sum it amplitudes for every destination sample-point. But this can be tricky when the ratio is non-integer.

In real live, you have to shorten the sinc-function by windowing (blackman etc) it to reduce the calculation time.
What i have done is, to build a oversampled + windowed sinc-table, and than take interpolated values from it.
If you promise to make an multi-process version from it (basically you only need to parallelize a for-loop), i can send you the code for free, as a starting point :slight_smile:
I will help to verify the result.

Basically this is what you need, take the dest-samples from the black line (but keep in mind that sinc-functions need to be bandlimited if dest-samplerate is lower)
Are you interested?


#4

Sure, if you have code to share, that’d be awesome.


#5

I sent you a mail.


#6

To help clear the air, I did that test for the SRC site, and used the ResamplingAudioSource. The other one did not exist at the time.


#7

Aleksey Vaneev has released his r8brain SRC code as open source, under a MIT license

https://code.google.com/p/r8brain-free-src/

http://www.kvraudio.com/forum/viewtopic.php?p=5460050

On the SRC comparisons website, r8brain seems to be very good, and the documentation cleams that it is also very fast !