Multi Channel File Mixing

Multiple-channel file mixing

FLAC files support up to eight channels and OGG Vorbis supports up to 255. It would be interesting to extend Mixxx to allow DJs to work with these channels individually within a virtual deck so as to be able to create live remixes from stems. Doing this from a single multi-channel file greatly simplifies the workflow and eliminates synchronization problems.

Overview of required changes

(Awaiting review from the Mixxx lead developer.)

• FLAC and OGG SoundSources need to:
• Be extended to work with up to 8 channels, correctly reporting the overall track length.
• Get meta-data for each (whether any are stereo pairs/other groups.) Limit Vorbis to 8 channels as well for now.
• TrackInfoObject needs to add a property for channel groups and get/set functions for it.
• Decks need to:
• Offer additional controls for each mono channel or channel group: Mute, Solo and Volume controls
• Tell the Analyzer which channel(s) to use for BPM detection
• Analyzers need to:
• Remove their assumptions of stereo, treating all channels as individual mono entities
• Handle channel groups from 1-8 channels and process each group as a single combined mono signal
• Report the number of rendered streams to the waveform renderer (Due to channel grouping, this may be less than the number of channels in the file.)
• CachingReader needs to be extended to support up to eight channels
• The GUI needs to:
• Include additional parallel summary waveforms for each mono channel or stereo pair
• Display Mute, Solo, Volume, and Pan controls as the Deck reports
• Overlap all (active) channels' waveforms in the detailed waveform display
• The waveform needs to change the way it renders to either 0 at bottom, |max| at top; or 0 at center, -max at bottom, +max at top. (Current is left channel from 0 at center to |max| at top, right channel from 0 at center to |max| at bottom.)

Sample multichannel files

Here are sample files that could be used for testing...

http://people.64studio.com/~daniel/DJ_Vadim-Saturday.ogg (lossy, 24.5MB)

http://people.64studio.com/~daniel/DJ_Vadim-Saturday.flac (lossless, 71.3MB)

These are made using the stem files from http://ccmixter.org/imaginashun dropped into Audacity, mixed down to four stereo tracks, then using the multichannel export option (in Edit -> Preferences -> Import/Export -> Use Custom Mix) to get 8 channel output files.

They are both 44.1KHz sample rate, 16 bit depth, quality setting 5. The Ogg file will play in VLC. The FLAC file does not, but it can be mixed down to stereo in Ecasound with:

ecasound -a:1,2,3,4,5,6,7,8 -i DJ_Vadim-Saturday.flac -a:1,2,3,4,5,6,7,8 -o alsa -a:3 -chmix:1 -a:4 -chmix:2 -a:5 -chmix:1 -a:6 -chmix:2 -a:7 -chmix:1 -a:8 -chmix:2