The MP3 Polyphase Filter Bank, About the filter, and a possible GPU speedup Options

[JacobG]

Hello!

For a completely different application, I designed a 32-sub band filter bank in matlab,
And implemented it in CUDA for a GPU.
It currently uses 64 filters, a single 64 point FFT, and the decimation\interpolation is by 32.
But this isn't really important since the CUDA implementation can easily be changed.

Since I read that the MP3 filter bank also divides the signals into 32 sub-bands,
I was wondering if my GPU filterbank can be used for MP3 decoding.

My questions are:
1. Is the total number of taps in the MP3 filter 512, or is it 512 taps in the filter in every branch (512*32 total)?
2. How good is the isolation between the different sub-bands? Do they overlap (One input frequency may have a response in more than one band)? Are "holes", which by I mean dead areas between the sub-bands, allowed?
3. Is this filtering considered an expensive operation in MP3 decoding? What are the time constants it operates in for lets say 512 samples-
mili seconds? micro seconds?
4. Does the format use a specific filter for the decoding? Is there freedom to implement the filter bank with a different structure?

Thanks for reading,
Jacob

[knutinh]

Perhaps GPU-based transcoding could be interesting. Doing 1000s of files in a batch means large potential for threading/vectorization.

-k