2.4.0: --insane output length wrong (silence added at both ends)

[gee-ell]

(first time I've tested 2.x)

windows 2.4.0 binaries: input: 96k / 64bit float

ssrc.exe --rate 48000 --bits 24 --dither 98 --pdf 1 --profile insane %1 "%outfile%"

= output is longer than the input, silence is added at both ends. example:

input: 1m 25s 68ms

output: 1m 27s 799ms

[gee-ell]

only seems to affect 'insane' profile, 'high' & 'long' give correct length output.

[shibatch]

This is not specific to the insane profile; silent intervals are added in all profiles. This is by design. They are added because FIR filters are applied during the resampling process. The insane profile is, literally, an insane profile, so various effects manifest in extreme forms.

[gee-ell]

OK but this isn't very useful, because the output then has to be trimmed back manually to the original length in most scenarios - it's better if the output is trimmed to the original length by default.

If you feel it's important to have 'correct' output padding from the FIR filters, this would be better as an optional switch.

[shibatch]

The question becomes how to define the correct output.
If you cut off the beginning and end of the output audio file, those parts will have incorrect characteristics.

[gee-ell]

right, but in any meaningful way? surely most or all of it is below the noise floor, or close to it. I'd be very happy trimming back to the original file, intuitively that's what you expect from a tool like this.

[shibatch]

What I'd prefer is not to trim it, but to add it to the previous audio segment. Since you can get the delay, that should be possible.

[gee-ell]

I'm not following you. maybe we're talking about different things.

I'm talking about the overall audio file, which currently has (effectively) silence added to the beginning and end, making it longer. intuitively, you expect the track length in comes out identically. that's also crucial for mastering, where people will not expect the already-decided metadata (ie. length in this case) to change just because the file is resampled.

in 'insane' profile this is more pronounced yes, but there it actually adds 1.3s of silence at the beginning, and at the end to my 1m 25s test file. that silence can be trimmed with no consequence.

[gee-ell]

[shibatch]

You might not notice it by ear, but a spectrum analyzer clearly shows distortion. Theoretically, each PCM sample has infinite length. Correctly converting the sample rate theoretically means generating infinitely long PCM data. The question is how long to truncate it. With the insane profile, this becomes quite long.

[gee-ell]

yes, but FIRs are already truncated because we care about what is practical, and almost all of the infinity is completely inaudible to us. In practice, my test file has unwanted silence at each end that I will trim away, and it will sound completely fine.

[shibatch]

So it's just not audible to your ears. It's truncating the FIR, but the length of the filter and the delay correspond. The insane profile uses a long FIR filter, so the delay also increases.

[gee-ell]

don't forget, the long FIR length does impact the existing audio content positively even after the output is trimmed, but it makes no difference to silence (or near silence) in any audible way.

[shibatch]

Try outputting in a floating-point format. That silent segment should not be true silence.