Gsoc2010 Dvs Mode

Adding a digital vinyl system (DVS) / external mixer mode to Mixxx (GSoC 2010 project)

Student: Bill Good
Mentor: Adam Davison

Abstract

Adding an external mixer mode to Mixxx will greatly improve Mixxx's ability to act as a part of a digital vinyl system. Mixxx's current method of achieving this involves diverting one deck to the main output, and the other to the headphone output, allowing the two to be mixed externally. However, no features, such as the equalizer, can be disabled. Benefits of disabling various features include increased CPU time for other threads, and UI recognition of unwanted features.

More info

dvs_mode has some good ideas, as does GSOC2010 page.
I'm bkgood on launchpad and freenode
To contact me by email, use my irc name @gmail.com

Current status

Digging through the mixxx code base to try to further figure out implementation details, plus learning a bit about how sampling (digital represenation of analog signals) works and skimming a book on Qt.

Specification

Use cases

DJ Joe doesn't like lugging around crates of vinyl or CDs, but enjoys using his vinyl turntables (or DJ CD players) and mixer. DVS mode will allow him to control Mixxx's playback with vinyl control, and then mix the outputs with his own mixer, his his own effect modules, etc.

Design

Currently, the sample buffers are only accessible to EngineMaster. These will be exposed via accessor methods so that SoundManager can choose between the master and headphone mixes or the individual samples. Changes made will be conscious of eventual merge of n-decks branch, i.e. will want to look at exposing the various decks using a CSAMPLE* EngineMaster::getDeckByIndex(uint index); method in place of

CSAMPLE* EngineMaster::getDeck1();
CSAMPLE* EngineMaster::getDeck2(); // etc

There is, of course, an upper-bound given the finite nature of PCI slots, USB ports, and sound cards, but a DJ could easily use four decks (8 channels) of output (of course, there's currently only 2 inputs of vinyl control... not sure if n-decks extends that). The other major aspect of the mode is UI, preferences will have to be extended to support routing audio to an external instead of using an internal mixer. This will likely include a bit of refactoring.