[FFmpeg-user] LFE channel + 10dB

Wiebe Cazemier wiebe at halfgaar.net
Sat Apr 13 15:30:54 CEST 2013

----- Original Message -----
> From: "Carl Eugen Hoyos" <cehoyos at ag.or.at>
> To: ffmpeg-user at ffmpeg.org
> Sent: Saturday, 13 April, 2013 1:46:22 PM
> Subject: Re: [FFmpeg-user] LFE channel + 10dB
> Wiebe Cazemier <wiebe <at> halfgaar.net> writes:
> > 1) As mentioned, does ffmpeg adhere to this and
> > allow connect 5.1 speakers to apply the boost?
> Please test and tell us!

This is harder than it sounds, because you don't know if the test file already compensates for it. The reference I mentioned says:

Calibration tests generally hide this 10dB difference; a basic pink noise test will contain a signal that should play at 75dB SPL for each channel. For the normal channels, that means a signal 30dB below full scale (105dB-30dB = 75dB), but for the LFE channel it is a signal 40dB below full scale (115dB-40dB = 75dB): 1/3 of the signal amplitude. If those test signals are used to calibrate the amplifier so they all output at 75dB SPL, then everything is set up okay. The LFE channel now has 10dB of extra headroom above the other channels and can produce the full 115dB SPL when required.

But, I will do my best to find out, of course.

I can tell you that the ALSA driver doesn't apply this boost to its .1 output (For my Audigy 2 ZS), because testfile [1] plays significantly louder when addressing the subwoofer.

[1] http://www.halfgaar.net/media/chan-id.zip

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