[pulseaudio-discuss] Is this possible? - 4.1 with filtered bass

Lennart Poettering lennart at poettering.net
Thu Dec 11 06:28:39 PST 2008

On Thu, 13.11.08 20:41, Dom H (speedsix.lists at googlemail.com) wrote:

> Hi all,
> I believe I'm correct in saying Pulse doesn't support DD/DTS
> passthrough (yet) so what I want my system to pass the decoded output
> to my amps analogue inputs. I don't think this is a problem but I want
> it setup in a way that mimicks my amps decoder and I'd like to know if
> it's possible.
> My amp is configured with 4 speakers (no centre) and each is set to
> what the amp calls 'small' i.e all bass output below the crossover
> frequency is passed to the sub ASWELL as the discrete LFE channel.
> Centre information is mixed into FL & FR speakers.
> Now I know a 4.1 setup is possible in Pulse with a config line like;
> load-module module-alsa-sink device_id=0 channels=5
> channel_map=front-left,front-right,rear-left,rear-right,lfe
> The problem is, I'm assuming this is passing full range signals to the
> main speakers and only the discrete LFE track to the sub, this also
> suggest to me that playing audio tracks that don't have a discrete LFE
> track (2ch music for example) would not output anything to the
> subwoofer?

In .13 we do not synthesize LFE anymore by default. Previously (and
still now if you enable some config option) we would mix LFE from all
other channels. We did never apply a lowpass however.

In .13 the LFE channel will thus only get silence if you play a stream
without LFE data and it is up to the hardware you have connected to
your sound card to synthesize it if it wants to.


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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