Default Sample rate for Pulse Audio/Jack etc.

[ttoine]

Len,

48khz is good for audio production, recording, etc... But think that most
of what we are listening, from audio cd to mp3, ogg, etc... are stored in
44.1kjz files. I often listen to 44.1khz music (pulse audio apps) while
having a jack session at 48khz or 96khz. It needs a lot more CPU than if
jack is in 44.1khz.

Today, the industry standards are 48khz and 96khz for music and films. Some
people will record at 292khz for oversampling, in order to play very slow
samples without problems. But think about the weight of files, the cpu
needed to handle them, and the cpu to handle low latency effects. It is not
time to set 96khz as default. And a lot of sound cards can just not run at
that rate.

The question is : are user of Ubuntu Studio using it only for multimedia
production, on brand new pc ? Or are they using it for common use too, and
how powerfull are their pc ?

Maybe we can let 44.1khz for Pulse Audio because most of what we are
listening to are this way. And when someone will work on an audio project,
then he/she will choose the good rate when starting jack. That said, Pulse
Audio is able to connect to jack very easily, no matter the rate.

Toine


Antoine THOMAS
Tél: 0663137906


2013/1/7 Len Ovens <len at ovenwerks.net>

> There has been an interesting discussion on LAU this past week or so about
> 48k vs 44.1k sample rates.
>
> I have in the past felt that an audio project meant for CD would be best
> to start with 44.1k in and continue as such till CD print. It appears that
> is not so for a number of reasons.
>
> - Both 44.1k and 48k support 20 to 20k hz. In order to do so they have to
> do some filtering. But in the case of the 44.1 the roll off has to be much
> steeper than with the 48k. This done in two places, in firmware on the
> audio card and in the analog circuitry as well. In the firmware the cost
> is 4X as much in cpu speed, and memory for the 44.1k as for 48k. The
> designers cut corners in this area for this reason. So 44.1k audio is not
> as good quality wise as it could be. The greater roll off in analog
> circuitry also demands more parts and if poorly done affects the in band
> frequency response as well. Even in a high quality converter with good
> quality filtering, the in band response will be affected to some degree.
>
> - At some point many sound card manufactures started to design with a
> single speed ADC/DAC... at (you guessed it) 48k. They already had a dsp in
> place for such things as on board synths and such, so they could use that
> for resample as well. Some of the resample setups were really bad and did
> not even keep stereo channels aligned (some sound blasters a while ago).
> The ac97 is designed this way too, But the Intel HDA, while using a 48k
> centric bus and clocking, does have the ability to have a codec run at
> 44.1k. The parts count to do it right is quite high though, so I am not
> sure if it is used in practice. In other words some Audio IFs are 48k
> already and converting to 44.1k on the fly.
>
> - Some audio hardware is 48k only. I have a built in mic like this, at
> 44.1k it pops and clicks it's way through. This is not quality HW
> obviously, but the manufacture seems to feel 48k is standard.
>
> - 48k has slightly lower latency (96k is much better, but adat IFs loose
> half there channels for example and cpu use goes up. Live digital mixing
> uses 96k for lower latency)
>
> - Ardour's export to 44.1k wav from 48k project does less sonic damage
> than using 44.1k in and less damage than one reverb use. The designer of
> one of the better resamplers says that resampling uses the same stuff as
> filtering. In other words a resampler is a digital low pass filter which
> happens to have a different rate out than in.
>
> - Ubuntu Studio supports video work where 48k is standard.
>
> For all of these reasons I think it makes sense to set Ubuntu Studio's
> default sample rate to 48k in Pulse Audio as well as Jack/Qjackctl. If I
> had control over the codecs and other hardware, I would certainly suggest
> 96k and be done with it. I would suggest that our -controls app allow
> setting the default higher (or lower) as well.
>
> I am not sure, but I suspect that the Win desktop defaults to 48k and that
> is why HW sometimes comes in 48k only. (though the HDA audio system is
> designed to handle more than one sample rate at a time in separate streams
> on the same device) That being the case, and as Linux and in particular
> Ubuntu is designed to run on HW made for win.... maybe 48k should be the
> desktop default (Pulse) in Ubuntu vanilla too. Things just might work
> better.
>
> Note to self... check how changing default rate in PA and Jack to 48k
> affects our current problems with starting jack while pulse is streaming.
>
> --
> Len Ovens
> www.OvenWerks.net
>
>
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