Re: [FFmpeg-devel] [PATCH] libswresample: avoid s16p internal processing format

[Michael Niedermayer <michael@niedermayer.cc>]

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On Fri, Jan 06, 2023 at 07:04:59PM +0100, Paul B Mahol wrote:
> On Fri, Jan 6, 2023 at 7:01 PM Paul B Mahol <onemda@gmail.com> wrote:
> 
> >
> >
> > On Fri, Jan 6, 2023 at 6:25 PM Michael Niedermayer <michael@niedermayer.cc>
> > wrote:
> >
> >> On Thu, Jan 05, 2023 at 11:08:25PM +0100, Paul B Mahol wrote:
> >> > On Thu, Jan 5, 2023 at 9:53 PM Michael Niedermayer <
> >> michael@niedermayer.cc>
> >> > wrote:
> >> >
> >> > > On Thu, Jan 05, 2023 at 01:44:10PM +0100, Paul B Mahol wrote:
> >> > > > Patch attached.
> >> > >
> >> > > >  swresample.c |    3 ++-
> >> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> >> > > > eee7a0685b44aa867562138a2e2437ecb8844612
> >> > > 0001-libswresample-swresample-avoid-s16p-internal-transfe.patch
> >> > > > From 9c4cd60e2dd41cf98d693c8251f4cfade0807073 Mon Sep 17 00:00:00
> >> 2001
> >> > > > From: Paul B Mahol <onemda@gmail.com>
> >> > > > Date: Thu, 5 Jan 2023 13:40:12 +0100
> >> > > > Subject: [PATCH] libswresample/swresample: avoid s16p internal
> >> transfer
> >> > > format
> >> > > >
> >> > > > Instead use float one by default for sample rate conversions.
> >> > > > The s16p internal transfer format produces visible and hearable
> >> > > > quantization artifacts.
> >> > >
> >> > > When does this occur and why?
> >> > >
> >> >
> >> > It occurs always. Just compare output with 16bit and int32/float/double.
> >> > Look at other people report on internet.
> >> > Look at src.infinitewave.ca
> >>
> >> src.infinitewave.ca uses 32bit none of what it shows should touch the
> >> codepath
> >> you change.
> >>
> >> if we look at src.infinitewave.ca for swr we see 2 types of artifacts
> >> 1. Aliassing which is at maybe -120db with the actual signal at 0db
> >>    i would like to see some evidence that a human can hear this
> >>
> >
> > For s16p<->s16p it is much lower, around -78dB thus this patch.
> >
> > Also for others and reports for swr its is lower than exact -120dB
> >
> >
> > 2. Reflection and attenuation at the transition frequency
> >> With linear filters there is a tradeof between attenuation of the
> >> passband, reflection of frequencies beyond, latency and so on
> >> You can have a perfect sharp cutoff with no attenuation and no refelection
> >> that requires a infinitly long filter. And while this looks best in this
> >> frequency plot, does it actually sound best ? If you can hear -120db
> >> signals you surely would then also hear the ringing long before a gunshot
> >> from such long filter.
> >>
> >
> One can always change linear FIR to be min phase FIR kernel.

I certainly would welcome a wider range of filters in swr, if you want to add
any low delay sinc approximation or in fact i would welcome any filter
you want to add.

thx

[...]
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