[jmarshall]

hi all,

i've just implemented preliminary 48khz direct digital output of pcm streams (and anything that decodes to 2 channel 48khz pcm such as mp3/ogg/flac/aac etc. etc.) into cvs.

this is an experiment to see whether adding our own high quality 44.1khz -> 48khz upsampling is worth the cost in terms of coding and the cpu performance hit.

i need people to test the quality of this.

to participate, please first obtain the ssrc.exe tool (windows command line tool) from here:

homepage of ssrc resampler program

next, do the following:

1. get a good cd track you wish to use for testing the quality.

2. rip it using eac or something you're confident with to .wav format.

3. next, run it through ssrc with the options:

ssrc --rate 48000 in.wav out.wav

you could add --dither 3 or 4, and --pdf options if you wish to see if these make a difference.

4. copy both files to the xbox and check you have dd/dts passthrough enabled (and digital out!. note you don't have to have a dd/dts decoder - just pcm is fine.

5. play both tracks - see which one you like the sound of better and report back here. note that you should be able to tell that the 48khz one is being direct passed through by watching a viz - not a lot should be happening if all is working.

note that i encoded both my files with flac in order to reduce the size and also i had a bit of trouble with .wavs causing crashes at the end of the track.

let me know how it goes. note that the direct digital output track has been attenuated by mplayer on playback in order to match the output from the mcpx audio processor on the xbox - this will, if anything, reduce the quality and dynamic range of the 48khz file.

i have tested norah jones "don't know why" but could not determine a significant difference, though i think i prefered the direct passthrough method. this may be because i was expecting it to be better, though!

let us know how it goes.

cheers,
jonathan

[pike]

i will test this later today!

like i wrote here ssrc is the way to go. low cpu usage and one (if not the) best resamplers available out there.

[MrMario64]

great, i will test this today to..
(though i will install an xboc with xbmc at a friends house to so hope i have the time )

[thebeast]

i wish i could test this, but i don't have digital output add-on or cool audio hardware yet. it sounds great though, lets squeeze everything audio out of the xbox hardware, that is possible.

and then a little more

[Butcher]

i will test this later today!

like i wrote here ssrc is the way to go. low cpu usage and one (if not the) best resamplers available out there.

only worth it if it's better than the mcpx though - as that is effectively no cpu.

[pike]

when we enabled passthru for dd, the difference was -very- noticeable

[Butcher]

true, but a dd resample is different from pcm stereo.

[pike]

ok, i _attempted_ to do the test but it was not possible due to:

the 44khz one, no problem (as expected)
the 48khz one, didnt make the slightest *beep*

it doesnt help that settings;music is quite "screwed up" at the moment

[pike]

true, but a dd resample is different from pcm stereo.

yeah, atleast 2steps less, no decoding/encoding (unless output to all speakers naturally)

[Gamester17]

[14:43] <poing> i'm not sure if a change jcmarsha comitted was intended to work like that, or if it's a bug
[14:43] <poing> stereo 48khz material is always output with passthru now
[14:44] <poing> ignoring the stereo passthru yes/no option

sound like a bug to me (sorry i don't have external amp/decoder so i can't test or confirm this, wish i had/could though)

[pike]

i'm starting to think my decoder doesnt like 48khz pcm streams... can't get passthru to work

[jmarshall]

pike: a lot of music dvds are 48khz pcm - do these work for you?

also, try viewing a viz while playing the 48khz track - it shouldn't do much (fountain.vis just has a single solid curve coming out from the centre that goes around and around the screen for instance).

gamester: poing has fixed that small discrepancy so that it only passes through now if the dd stereo pass through is enabled. (obviously this option is now misnamed though . once we've determined whether our own upsampling is worth it or not, i'll look at overhauling the options so they are a bit more clear.

cheers,
jonathan

[jmarshall]

the only advantage i see currently with doing the software upsampling currently is the 6db hotter output. if this can be achieved through the mcpx though, it will be negated.

i find no obvious quality difference, though i'm going to get some better samples for testing before i make my final conclusion.

cheers,
jonathan

[Butcher]

try idirectsound8:etmixbinheadroom for boosting the output by 6db.

[jmarshall]

thanks butcher - after the discrepancy in volume came out to almost exactly 6db, i figured that the mixbins process was leaving some headroom in there somewhere. will try it out tonight.

i got a "killer" sample from hydrogenaudio.org that i'll test when i get home - makes it easy to detect poor upsampling and/or clipping. will see how it goes tonight.

cheers,
jonathan