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single-deck_vinyl_control [2011/03/07 15:37]
single-deck_vinyl_control [2011/03/07 15:49]
ywwg filled out the page based on how the feature actually works
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 ===Toggling Between Players=== ===Toggling Between Players===
 +  * How does Mixxx know which player should be controlled by the timecoded vinyl?
- * How does Mixxx know which player should be controlled ​by the timecoded ​vinyl?+Single deck mode works by setting both decks to use the same audio input. ​ The DJ then alternates activating ​vinyl control on one deck, then the other. ​ This feature is designed so that when deck control is disabled, playback continues without interruption.  ​
-> Via a button on the interface ​and/or hotkeys. ​ When it'​s ​depressedthat player receives timecode signals.+It is theoretically possible to mess up and activate vinyl control for both players, and thus have vinyl input affect two decks at once, but in practice ​it'​s ​easy to turn off control on one deckand on on the other.
-a good default key would be the space bar. since this would be the most used function in a single ​deck setup.+It is also possible to forget that you've changed ​the pitch on the turntable, and reenable control on an old deck.  The playback speed suddenly changes, with disastrous DJ-fail results. ​ Just don't do that.
 ===Indicating Active Deck=== ===Indicating Active Deck===
-in a single timecode setup it is essensial ​that it's really obvious to the user which deck is under timecode control. +With the new vinyl code, there is a special vinyl status light that can indicate much important state information. ​ A solid green indicates "​active,"​ for instance. ​ With single deck mode, the DJ looks for which deck has an active ​indicator lit.  The indicators should be large and prominentmaking it easy to see at glance which deck is active.
-either by changing the colour of the active ​deckor with big symbol appearing over the active ​decks waveform. +
- +
 === Preferences Dialog Considerations=== === Preferences Dialog Considerations===
-  * There should probably be some "​single-deck mode" checkbox in the vinyl control preferences that greys out the second input combo boxes and enables this feature. Whatever the prefs dialog modifications end up being, they'​re probably contingent on the "​Toggling Between Players"​ design above. 
 +  * Setting up single-deck mode is as simple as choosing the same sound device as the input for both decks. ​ There is no special "​single deck" button needed.
 ===Internal Changes=== ===Internal Changes===
-In soundmanager.cpp,​ specifically in SoundManager::​setupDevices(),​ there is the following snippet: +  - I enabled ​the ability ​for two decks to share an input 
- +  - I added enable/disable buttons ​for each deck 
-      //​Initialize vinyl control +  - I ensured ​that playback would continue once vinyl control ​was turned off
-      m_VinylControl[0] = new VinylControlProxy(m_pConfig,​ "​[Channel1]"​);​ +
-      m_VinylControl[1] = new VinylControlProxy(m_pConfig,​ "​[Channel2]"​);​ +
- +
-Each physical turntable'​s audio gets passed off to a VinylControlProxy object to be processed. The VinylControlProxy/​xwax/​scratchlib object then manipulates Mixxx'​s internal pitch and playback position. The channel string parameter tells each VinylControlProxy object which player it should be connected to. From that string, the VinylControl class constructor grabs "​ControlObjects"​ which allow it to hook into Mixxx'​s various internal controls. For example, inside the ''​VinylControl::​VinylControl(...)''​ constructor,​ you will see: +
- +
-  playPos ​            = new ControlObjectThread(ControlObject::​getControl(ConfigKey(group,​ "​playposition"​))); ​   //Range: 0.0 to 1.0 +
- +
-That "​playPos"​ object then allows the VinylControl object change the playback position (eg. when needle dropping) ​for the player specified by "​group"​ (which would be [Channel1] or [Channel2]).  +
- +
-In order to allow a single deck to control either player/​channel,​ one could modify VinylControl/​Proxy and allow it to get the ControlObjects for the other channel (this is the hard approach). An **easier approach** is to keep all the VinylControl objects the way they are, and to simply route the audio to the correct VinylControlProxy object depending on whichever player is supposed to be controlled. +
- +
-The starting point for this way would be to look at SoundManager again: +
- +
-  ​CSAMPLE * SoundManager::​pushBuffer(QList<​AudioReceiver>​ recvs, short * inputBuffer,​ +
-                                      unsigned long iFramesPerBuffer,​ unsigned int iFrameSize) +
- +
-This ''​SoundManager::​pushBuffer()''​ function gets called when a soundcard has given Mixxx (input) audio to be processed, like from a timecoded vinyl. Near the end of the function, you'll see the code: +
- +
-<​code>​ +
-        QListIterator<​AudioReceiver>​ devItr(recvs);​ +
-        while(devItr.hasNext()) +
-        { +
-            AudioReceiver recv =;​ +
-            if (recv.type == RECEIVER_VINYLCONTROL_ONE) +
-            { +
-                //​recv.channelBase +
-                Q_ASSERT(recv.channels == 2); //Stereo data is needed for vinyl control +
-                if (m_VinylControl[0]) +
-                    m_VinylControl[0]->​AnalyseSamples(vinylControlBuffer1,​ iFramesPerBuffer);​ +
-            } +
-            if (recv.type == RECEIVER_VINYLCONTROL_TWO) +
-            { +
-                Q_ASSERT(recv.channels == 2); //Stereo data is needed ​for vinyl control +
-                if (m_VinylControl[1]) +
-                    m_VinylControl[1]->​AnalyseSamples(vinylControlBuffer2,​ iFramesPerBuffer);​ +
-            } +
-        } +
-</​code>​ +
- +
-This code demonstrates of how the "​routing"​ of the input audio works. Each SoundDevice object has a list of AudioReceivers in it, which you can think of as the things that it's going to pass its input audio to. In this code snippet, you can see that if the SoundDevice has an AudioReceiver of type RECEIVER_VINYLCONTROL_ONE,​ then that audio will be passed off to the first VinylControlProxy object and it will control the first player. If we want single-deck vinyl control, we need to modify the list of AudioReceivers inside a SoundDevice at runtime so the soundcard controls the desired player. +
- +
-If you look at SoundDevice.cpp,​ it looks like you can do this with ''​SoundDevice::​addReceiver()''​ and ''​SoundDevice::​clearReceivers()''​. This is roughly the end of the string here. **As a starting point, look at ''​SoundManager::​setupDevices()''​ and check out the ''​addReceiver()''​ calls in there.** +
- +
- +
-===== Work Breakdown ===== +
- +
-This [[http://​​wiki/​Work_breakdown_structure|work breakdown structure]] (WBS) outlines the work that needs to be done to complete this feature: +
- +
-  ​1. Single-deck vinyl control +
-    1.1 Assess existing vinyl control code +
-      <​del>​1.1.1 Write internal changes section for wiki</​del>​ +
-      1.1.2. Figure out how exactly we want to make control switch from one player to another. +
-    1.2 Modify existing vinyl control code +
-      1.2.1 Read from crossfader (or whatever) ControlObject to determine which player to control. +
-      1.2.2 Change the AudioReceiver for the soundcard ​that's opened for input, depending on which player should be controlled.  +
-    1.3 Modify preferences dialog +
-      1.3.1 Add single-deck ​vinyl control ​checkbox +
-      1.3.2 Make the checkbox grey out the second input comboboxes.  +
 +Basically I rewrote a lot of stuff.
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 If you're interested in helping to code this feature, sign up your name below: If you're interested in helping to code this feature, sign up your name below:
-  * Josh Matthews 
-  * Luis de Bethencourt 
   * Owen Williams (is actively working on this issue in his tree: lp:​~ywwg/​mixxx/​features_xwax2)   * Owen Williams (is actively working on this issue in his tree: lp:​~ywwg/​mixxx/​features_xwax2)
single-deck_vinyl_control.txt · Last modified: 2013/04/30 07:35 by jus