Works perfectly hahaha!
By officializing I meant creating a real plugin, like this. hahah
Thanks 
Thank you Steve for the plug-in (our first cooperation…).
Due to the shrinking process of the code, there is now a lot of space for an additional low pass filter…
Thanks for the Bequat filter link, I am still admiring the code, though I am no fan of the analog inspired filters. All those coefficients are rather egyptian hieroglyphs for me. Well, that’s not exactly true, since I know a few hundred of the later ones but you certainly grasp the meaning. Anyway, there is a lot of room for experimenting in this area, as mentioned before. Especially unwanted side effects of resampling are most interesting from a musical point of view.
Here is a sample of WAV compression on 1kbps—128kbps: https://www.youtube.com/watch?v=orvhDLVcvks
How I made this (not necessarily in the same order for independent operations): You may be tempted to understand Roman language and say X is 10, but not so. X is one of the items of the set of 8 frequencies from 250Hz to 32000Hz, in exponential increments of 2x.
In OpenMPT, I first upsample the 44100Hz song to a multiple of X with a high quality algorithm. This means 44250Hz, 44500Hz, 45000Hz, 46000Hz, 48000Hz or 64000Hz. Then I downsample with Nearest Neighbor to X. I save the result. The first step of compression is done.
Then the resulting sound is open in Audacity. I save it with IMA ADPCM — but sometimes I have to repeat this, as I fall for the trick of the Project Rate number being different. The second step of compression is done.
I repeat it for all 8 values of X. This will give me a set of WAV sounds from 1kbps to 128kbps.
Post–processing: They are opened in OpenMPT. I upsample each of these to 48000Hz with Nearest Neighbor. In case of X being 32000Hz, this will lead to samples alternating between being once and twice. I’m not a “bouncing frequencies” expert, but I don’t think it (half–integer upsampling) causes major distortions as opposed to integer upsampling with Nearest Neighbor.
Then I cut first 15 seconds from them, and combine them. I add labels. I record a video. I upload it to YouTube.
where do you make the “polynomial” one?