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Interview with Lennart Poettering (LinuxFR.org)

Interview with Lennart Poettering (LinuxFR.org)

Posted Jul 6, 2011 17:19 UTC (Wed) by alankila (subscriber, #47141)
In reply to: Interview with Lennart Poettering (LinuxFR.org) by helge.bahmann
Parent article: Interview with Lennart Poettering (LinuxFR.org)

As an aside:

It's said that for FIR filters, you can select control of phase, frequency response or latency, but not all simultaneously. Typically, SINC kernels are arranged with the best possible frequency response and linear phase characteristics. However, it's possible to give up on the linear phase property to reduce latency.

Normally SINC is a symmetric filter with mirrored halves around its midpoint, and the large values of the kernel occur at the midpoint. Therefore, at 256 taps it causes a delay of about 128 samples, with about 128 samples of ringing around the midpoint of the action of the filter kernel.

A minimum-phase reconstruction of the same filter can probably reduce the latency to just a few dozen taps, because the large values of the sinc kernel are arranged to happen as early as possible in the filter. The ringing, then, takes the rest of the kernel and has somewhat larger amplitude.

I don't think the human ear is sensitive to phase at all, especially at the highest frequencies, so I'd love if more people at least considered minimum phase filters.


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Interview with Lennart Poettering (LinuxFR.org)

Posted Jul 8, 2011 0:52 UTC (Fri) by HenrikH (guest, #31152) [Link]

>I don't think the human ear is sensitive to phase at all

I might be reading you wrong, but the human ear is very sensitive to phase. For example phase is how the old Dolby Surround provided more channels than speakers.

Interview with Lennart Poettering (LinuxFR.org)

Posted Jul 11, 2011 10:05 UTC (Mon) by alankila (subscriber, #47141) [Link]

Yes, that's not what I meant. Phase is important when it comes to coherence of several channels, but if you process all channels with a similar transformation, people aren't usually able to notice.

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