Hello you musicologists !
I like to create karaoke video files, to sing with my friends.
Sometimes we need to modify the pitch of the music, for instance from F# to Ab.
Is it possible to transpose directly in the ac3 file, or am I obliged to convert it to a wav file, transpose with audacity, and then remux it ?
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(Again with the musicologist? )
Do you intend to modify AND THEN RESAVE? or just modify DURING PLAYBACK?
If only during playback, there are media players that allow pitch transpose (Google: "music playback pitch transpose" and you should find some, including foobar2000). Audio tracks within video might be more difficult, but not impossible (can do "AssumeSampleRate()" in AVISynth, for example).
If intending to resave the file for future use AS TRANSPOSED, you will HAVE to decode, transpose & re-encode the file (losing quality). And if these are video files, you would also have to demux first & remux again later.
Note: most pitch processes you find in video-centric, or in consumer-music-centric, apps do not include formant compensation nor time compensation, so if you double the pitch (octave higher), you are also doubling the speed of the music (cutting play time in half) as well as making it sound like a chipmunk. Conversely, halving the pitch (octave lower) would double the play time (S-L-O-W speed) and making it sound like a drunk Darth Vader. Also note, that, whether playing live or processing and resaving, if you have corresponding video to your audio, you will have to ALSO adjust the speed of the framerate of the video to match in order to keep the V+A in sync.
Luckily for your example, an F# to Ab is only 2 semi-tones, so the change isn't going to be too drastic.
I never thought of mofications during playing, it could be a good option when my fiends have a PC connected to their TV.
But I prefer not to take the chance, and save everything on DVDs.
I found a method, rather long, but efficient :
Convert ac3 to Wav,
Open Virtual XP on my Windows 7 Pro
Modify the tone
Save the wav files
Convert them to ac3
Thank you for your advice about the lengthes that could have been modified. Luckily, Wavelab keep the speeds.
Have a nice texan day