Convolution filtering

[Alandbush]

Quote:... perhaps this samples value of 32768 should reflect the number of samples/taps used to generate the convolution file.

I have repeated the tests I conducted yesterday with the same favourable results.

I used a couple of tracks from Janet Jacksons' All For You album.
Track 10 Lame ends with the word 'see' and track 11 Trust a Try begins with the word 'trust' and these tracks would normally segue with no gap.
I used a 32768 tap FIR LPCM wav file, generated by Rephase, in the streaming options together with the pad and trim values also set to 32768 samples.

Playing these tracks in sequence, it is clear to hear the truncation of both words of these tracks, albeit with an almost non existent gap of silence.
Changing the pad and trim values up and down would either reduce the truncation of the words, but not eradicate it, or reproduce the click between the tracks.
Eventually, I found the perfect value which produced a stream of audio almost indistinguishable from the non-convoluted stream.
This value was 16384, half the value of the 32768 tap file. Coincidence?

I repeated the tests but this time with a 65536 tap filter and found that the perfect pad and trim value was 32768. Not a coincidence.

At this point, I recalled that Rephase offers an option to 'centre' the start of the impulse response within the FIR file. The default option was set to middle and Rephase reported the IR offset as 16384 after generating the 32768 FIR file.

Unless I am completely misinterpreting all of the above, I have concluded that the FIR generated by Rephase contained nothing significantly useful in the first 16384 samples. These insignificant samples are duly reflected at the beginning of the convoluted output file and therefore removing these samples does not affect the audio content. I do not, however, have any explanation regarding the padding other than knowing that without it the word at the end of track 10 is truncated.

I'll end by stating that my comprehension of convolution is very, very basic and I do not understand the 'magic' that occurs when applying the pad and trim values. It is purely based on the above listening tests.

nb - FIR filters generated by other products may be similar to Rephase with regards to the impulse response offset but YMMV.