Re: [LAU] How do i play 24/96 and 24/192 bit files at native rates and verify that it's happening?

On 12/26/2009 10:05 AM, Bearcat M. Sandor wrote:
>> Paul, I think either you misread him a bit or I did.
>>
>> My quick and dirty read follows:
>>
>> I think what is basically wants is for the system to determine the one files
>> is in format Y and set up HW to match. The another file is determined to be
>> format Z and sets up HW to match so that at all times, if possible, what is
>> being sent to the card matches what the card is configured for.
>>
>> It seems he knows this will not be able to happen for 44.1 or below as his
>> card only goes down to 48.
>>
>> Does this seem possibly what is being asked on a re-read?
>>
>>
> Thanks Drew and Paul,
>
> Heh. Let me restate it by addressing what i want. I want 24/96 and
> 24/192 played at full quality:
> 1) I play a 16/44.1 file. It's upcoverted to 24/48khz which is the
> card's lowest rate. I don't have any choice in this matter
> unfortunately.
> 2) I play a 24/96 file. The data stays at 24/96 and is not converted to
> 24/48.
> 3) i play a 24/192 file. The data stays at 24/192 and is not converted
> to 24/48.
> 4) If the above is not possible, i'll upconvert everything to 24/192.
>
> I'm using MPD for playback, pulseaudio for a sound server and alsa. I
> would like it if it were the case that they just passed it along the
> chain and it were played in it's native format, and no special
> configurations were needed to accomplish that. Is this the case? If not
> what special considerations for configuration should be taken into
> account.
>
> If it's not the case that the files bit-rate is untouched by mpd, pulse
> and alsa, each of those programs/libs have settings that can force
> change the bitrates for all input to a single rate. If they can't just
> pass it along i'd choose to change the rate to 24/192 for all files.
> Would i only have to change settings in one of those or all three? If i
> change MPD to upconvert to 24/192 will pulseaudio or alsa just reformat
> it back to 24/48?
>
> To put it another way, if i had a sacd player it would be sending data
> at bitrates that correspond to what's on the disc, not downsampling
> things to 24/48. I want to do that with my music files too using my pc.
> I know that some sacd players like to upsample everything to 24/192. If
> that's the only way to do it to play all files at no less than their
> native bitrates then i'll do that.
>
> I have a quadcore at 25.ghz and 8 gigs of ddr3 ram so my system should
> be able to handle the overhead.
>
> I can explain it another way if need be.
>
>

pulseaudio and jack work by using one sample rate and it is up to the
client side to conform to it.

If you want to bypass that limitation you either need to write a new
sound server or extension to the existing servers to allow switching to
different sample rates on the fly* or go directly through alsa.

* IIUC, jack already supports this concept in the backend so there is a
good place to start.

Afaik noone has written an app to allow jack to be switched
automatically to the different sample rates based on the sample rate of
the file being played. Obviously even if this was the case you would
only be able to play one sample rate at a time so if you have multiple
files with multiple sample rates then you would only be able to play
them one at a time.

If you use the plughw interface for jack you get automatic sample rate
conversion handled by alsa but that is on the client side so your
24/192 wil be converted to 24/48 before being output which is the
opposite of what you are asking.

-- 
Patrick Shirkey
Boost Hardware Ltd
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