Beatloops

Summary

Status: There is a branch which has most of these features implemented. Testing is still needed.

Mixxx has BPM detection but not beat detection. Beat detection would allow us to do man cool tricks including:

Jump from beat to beat
Quantize Effects
Create Beat Quantized loops
Do full Automatic Beat Syncing
Beat Smashing/Splicing (ala Aphex Twin)

Current Status

There is currently a branch at https://code.launchpad.net/~mixxxdevelopers/mixxx/features_beatcontrol.

Current Status:

[ChannelN],beatloop CO implemented
I've also implemented [ChannelN],beatloop_(SIZE) CO's for skins. Need to reimplement a thread safe version of QSignalMapper.
[ChannelN],beatseek CO slated for another release

Design

Most of these features use Engine Controls which interact and communicate amongst each other. Beat loops, for instance, are done by querying the track's beats and then setting the loop in and loop out positions with that information.

Beat loops

I use both a straight [ChannelN],beatloop CO which will take the argument in set as the number of beats the loop should have. Fractional and negative values work.

The behaviour of beat loops varies whether or not the value is above or below zero (absolute) and whether it is positive or negative.

If the number is not a fraction and is positive it will create a loop starting at the next loop and ending N loops after.
if it is a fraction it will end the loop at a fraction of the beat's length after the next beat.
If the number is negative it will set the end of the loop at the next beat and the beginning at N beats before.
if it is a fraction it will begin the loop at a fraction of the beat's length before the next beat.

Beat Seeking

Beat seeking is done by calling the [ChannelN],beatseek CO and setting the value to the number of beats to jump. The jump will occur on the next beat.

Quantization for Loops, Cues & Hotcues

I have added a new Engine Control; QuantizeControl, which has the following CO's:

[ChannelN],quantize: enables quantization on the deck.
[ChannelN],quantize_beat: is always set as the next beat if quantization is enabled.

It also has a pushbutton, for skins; [ChannelN],quantize_enable.

These CO's are then queried when setting up loop points and cues. If quantization is enabled, ie: [ChannelN],quantize == 1.0, then the function queries [ChannelN],quantize_beat and uses that as it's new position instead of the current play position.

Controller Object Table

Group	Name	Parameter	Values	Notes
[ChannelN]	beatloop	The number of beats to loop over	N/A	Loops from next beat to N backwards if negative. works with fractions.
[ChannelN]	beatloop_X	(Push Button)	N/A	Loop over set number of beats, for X = { 0.0625, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64 }
[ChannelN]	quantize	Enable or disable	Enabled?	Boolean for turning on/off quantize mode
[ChannelN]	quantize_beat	Next Beat to Quantize to	Frame	Returns the Frame offset for the next beat.

New Controller Objects being worked on

Group	Name	Parameter	Values	Notes
[ChannelN]	loop_size	Size of loop in beats	float	Used for output and can be manipulated by script(might not be safe)
[ChannelN]	loop_double	On/Off(PushButton)	boolean?	Double the loop_size, as of now can go beyond track limit(and overflow), but safely degrade by playing logic
[ChannelN]	loop_half	ON/Off(PUshButton)	boolean?	Halfs the loop_size, hardcoded limit on 1/64 of tracks beat size