how to change the tempo of a 5.1 flac?

[SteMa]

I have a 5.1 ch flac track, that syncs with a 23.976 fps video, which I want to speed up to pal (25fps). I would like to increase the tempo (speed up without changing the pitch) of the audio (25000/(24000/1001)). I tried several things, like avisynth, which gave way less than desirable quality. Someone suggested audacity, which uses an awful lot of space, and while it can import multichannel flac, it can't export multichannel to any format, only separate channels. So I have 6 mono waves, that I want to merge into a new flac file (I don't know the quality yet). But something better would be welcomed, something that would change the tempo and saving it right into flac. A commandline program would be the best, or a good quality avisynth tempo changer would work too, since I can import flac and export it too with soundout().

[ACrowley]

You can use Audacity 1.3 to decompress 16/24bit FLAC 5.1 to 6 mono Waves ( with correct output channelmapping)
Simply open flac Audio with Audacity 1.3 and decompress it to (mono) Wave.

Then use a Waveeditor like Nuendo/Wavelab/Adobe Audition/Nuendo to adjust Tempo

23.976 to 25.000 = 95.90404%
25.000 to 23.976 = 104.27094%

Ofcourse you can do it with Besweet/Audacity, but theres a Test on another Site, and Audacity and Besweet are not recommended
http://www.hydrogenaudio.org/forums/lofiversion/index.php/t21704.html

I pers. use or SteinbergNuendo3.2 (standand Algor) It Delivers good quality and is fast.
Ofcourse mpex2 Algorithm is the Optimum, but it takes to long(6 mono 5-8h). Standard Algorithm, is a good Compromise and quality should be similar to Audition/Wavelab/Soundforge

At last load the new 6 mono waves into Audacity again and reencode it to flac. Or merge them with wavewizard and use flac.exe/Mediacoder
Ofcourse it will take a lot of Discspace when you work with uncompressed Audio :)

Other Method :
Simply change the Framerate from your Video. When its mkv ,just remux in mkvmerge it with a Timecode.txt File and it will change the Video Framerate lossless

greets

[SteMa]

Thanks, I'll have a look at that neundo. I don't care if it takes all night to convert all channels, my computer is turned on anyway. Can it handle 6ch flac as input and 6ch flac as output?

edit: by changing the timecode, the video only gets out of sync. I will change the fps to 25, but I need to adjust (stretch) the audio to sync with it. Setting the timestretch in mkvmerge only gives jumps in the audio (well that was the case with ac3s at least).

[madshi]

Ofcourse you can do it with Besweet/Audacity, but theres a Test on another Site, and Audacity and Besweet are not recommended
http://www.hydrogenaudio.org/forums/lofiversion/index.php/t21704.html
IMHO this test is more or less invalid. Personally, I'm a PAL guy and I often convert PAL audio tracks back to 23.976. The very important thing to note here is that by far most PAL tracks have higher pitched sound. That means the conversion done by the studio from 23.976 to 25.000 was done ***without*** pitch correction. Most studios are doing it this way because doing pitch correction can cause other ugly sound artifacts. But what this means is that if you want to redo this conversion you MUST NOT use pitch correction, or else the final result will have lower pitched sound than it should have! Because of this fact the test done on that hydrogenaudio site is more or less useless, because it aims at doing pitch correction and gives best ratings to those algorithms which do pitch correction. But if you want to undo the PAL speedup your needs are very much different and the simplest tempo change algorithm (without pitch correction) is actually the way to go. The open source tools do that just fine and AFAIK there's no quality difference between the tools, because the tempo change without pitch correction is a rather simple thing to do.

Ok, now this thread is not about undoing PAL speedup, it's about actually doing PAL speedup. In this case you have to decide for yourself if you want to use the same method the studios are using, namely *not* using pitch correction. Or if you want to use one of those pitch correction algorithms. That's your call. In the first case any open source solution which doesn't apply pitch correction should do just fine. In the latter case you should invest time into finding the best possible algorithm/software, because good pitch correction is very difficult to do and there are noticable quality differences between the different algorithms/applications.

[SteMa]

MPEX3 algorithm sounds fine, and there should be differences between not corrected algs. too, like there are many different image resizing methods. Since it's and HD video the 23.976fps is very low :( speeding it up a bit helps the motion to be more fluid, and we usally watch the movie dubbed, so I want that track to be untouched. The pitch differences are inaudible when not comparing directly, so maybe I stick with method w/o pitch correction. Thanks for your help too!

[ACrowley]

yes...madshi youre right. Dont thought about this Point of View.
Otherwise the guy simply compared the correct length of the output, and Besweet/Audacity are not exact enough (in his Test)

However, i always use Nuendo3.2 in standard Mode , it keeps full tone Pitch, no Pitching/Resampling, as like as Wavelab/Audacity

SteMa you can simple use Audacity for the full Process, should be no Problem
-Open flac in Audacity 1.3. It will decompress it to 6 mono waves
-your editing ntsc - pal
-Export it to Flac 5.1 again

In this more or less simple Cases with NTSC-PAL Conversions ,Mpex2/3 Algorithm is not worth it, imho.
Processing Time with mpex2 is painfull long for 6 mono waves.
Mpex2 in Nuendo or TimeFactory on 6 mono waves takes ~5h-7h (120min wave). Standard Mode only ~12-30min

Greets

EDIT :
Steinberg Nuendo always use pitching Correction ! For example when you make a Pal to Ntsc Timestretch the is still in PAL Pitch so Nuendo Algorythm use Pitching Correction. I pers switch to Behappy ( no pichtig Correction) and the reencoded pal to ntsc Audio runs corect at ntsc pitch without pitching correction from Timestretch (=better, imho)

[SteMa]

the best quality took about 3hrs with timefactory (114min wave), and the results are near excellent (sennheiser hd515), maybe a bit loss in dyncamic range for high frequency parts (mainly speech), but it's possible I'm hallucinating of those many comarisons :D The differences are really negligible! With audacity the voices had very much echo, and didn't sound nearly as clear as the source. If I download the lossless track, it deserves the best possible method :) Thanks for the help, the results are great :)

BTW, this made me wonder how good can besweets' fps conversation be? :/