On Fri, Jan 6, 2023 at 6:25 PM Michael Niedermayer <mich...@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 < > mich...@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 <one...@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. > > also what actually is the optimal frequency response of this filter ? > with a 22khz cutoff, a 22.1khz sine should be silence is that > really subjectively better than a 21.9khz sine ? > Iam not sure about this. Has someone done actual hearing tests with > actual real audio? the sinc filter originates from the idea of lossless > reconstruction of frequencies below nyquist if iam not mistaken, but humans > are not trying to losslessly restore a block of frequencies. A human > listener > generally wants to enjoy listening to some media. Has someone looked into > what is actually best for that real use case ? > This question matters because with it we can tune the filter parameters to > target humans. > > But lets push the doubts about choosing resampling purely based on > frequency > analysis away. > swresample has several parameters with which you can tune this: > we have a filter_size, if thats bigger you should get closer to the ideal > sinc. Theres phase_shift which may reduce the (i assume) unhearable > aliasing. > And cutoff which should allow to tune the (i assume) hearable > reflection/attenuation tradeoff also theres filter_type to allow you to > tune the > window function. > > If there are issues reported by people using their ears, please provide > more > details, iam interrested in these cases. > > > > > > > > > This change should be limited to the case that benefits, this would > force > > > this > > > even without resampling in some cases. > > > > > > > It is forced only if sample rates between input and output differs. > > If iam not mistaken it affects rematrixing without resampling too > How so? I really doubt that this patch do that. > > thx > > [...] > -- > Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB > > The real ebay dictionary, page 1 > "Used only once" - "Some unspecified defect prevented a second use" > "In good condition" - "Can be repaird by experienced expert" > "As is" - "You wouldnt want it even if you were payed for it, if you knew > ..." > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
