[pulseaudio-discuss] Bass management (Alexander E. Patrakov)

Christian Weinz christian at madez.de
Tue Sep 26 20:25:33 UTC 2017

> Date: Sat, 23 Sep 2017 18:59:58 +0500
> From: "Alexander E. Patrakov" <patrakov at gmail.com>
> To: General PulseAudio Discussion
> 	<pulseaudio-discuss at lists.freedesktop.org>
> Subject: Re: [pulseaudio-discuss] Bass management
> Message-ID:
> 	<CAN_LGv1pGJmPQ7Hr43NOLs8H6YLzO=nk8nLgzK4DExjFV1cSqw at mail.gmail
> .com>
> Content-Type: text/plain; charset="UTF-8"
> 2017-09-22 22:12 GMT+05:00 Christian Weinz <christian at madez.de>:
> > Hello,
> > 
> > I use headphones, and have tactile transducers on my chair. This
> > makes
> > the audio sound louder and feel more intense. This is good for my
> > ears
> > and my neighbours.
> > 
> > This setup requires 2.1 output. I tried the GNOME-Settings to set
> > the
> > output to 2.1. That option was not available. I also tried
> > alsamixer,
> > paprefs and pavucontrol, to no avail. I played around with
> > hdajackretask, and finally, after overriding both the Pink Mic port
> > to
> > Center/LFE and the Blue Line In to Back, I can select 2.1 audio in
> > the
> > GNOME-Settings. This was difficult to setup.
> > 
> > Then, however, I had the full-range signal on both my headphones
> > and on
> > the synthesized LFE channel. This means I hear voices in my chair.
> > To
> > prevent that, I set the lfe-crossover frequency, but then I lose
> > the
> > bass in my headphones. Both is bad.
> Thank you for accurately describing the frequency responses both of
> the headphones and the transducer. In particular, for confirmation
> that there is a significant overlap, which is the necessary condition
> to make sure that what we'll design will work not only for your
> hardware.

The transducer and the headphones do overlap significantly, for
otherwise I would just use the lfe-crossover-freq option.

I'm fine with a text-based, hand-tailored configuration.

> > Now I found the patch "Add option to disable highpass-filter on
> > non-lfe
> > channels." by Markus Ebner at
> > 
> > https://pw-emeril.freedesktop.org/patch/171424/
> > 
> > This patch, if it works at advertised, would solve my problem. But
> > the
> > patch was rejected. I would comment there, but because the websites
> > certificate is invalid, I cannot create an account to comment,
> > since
> > Google's reCAPTCHA refuses to work.
> > 
> > To summarize, for my setup I need the full-range stereo signal on
> > my
> > headphones and a low-pass filtered LFE signal for the transducers.
> > Is
> > there a way to do this with PulseAudio?
> The patch will not solve your problem acceptably, because the low
> frequencies from the headphones and the transducer will not be
> in-phase, due to the delay created by the filter.

I only hear the sound from the headphones with my ears, and only feel
the sound from the transducer with my lower body, torso, and arms. In
other words, I sense the signals with different senses. This suggests
phase correlation is irrelevant.

Of course, if the delay created by the filter became too big, then one
can notice the delay between the tactile and auditory sensation.
However, the just noticeable difference for temporal order judgments to
pairs of auditory and tactile stimuli was found in 1961 [0] to be
20ms, but was found in newer studies to be 80ms for inexperienced
participants and 40ms for more experienced psychophysical observers

Best regards,
Christian Weinz

[0] Hirsh I.J, Sherrick C.E. Perceived order in different sense
modalities. Journal of Experimental Psychology. 1961;62(5):423–32.

[1] https://www.ncbi.nlm.nih.gov/pubmed/15698825

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