PyKaraoke doesn't currently support pitch-shifting natively during song playback, and this is about the only missing feature that prevents PyKaraoke from being a complete digital replacement for the traditional analog CD+G player.
This is the case because PyKaraoke relies on Pygame's MP3/Ogg/WAV playback engine, which does not (currently) provide any means of applying effects filters to the sound before it hits the sound device. It would be possible to replace this with our own threaded MP3/Ogg/WAV player, and use libsoundtouch to perform pitch-shifting (it is a very high quality, faster-than-realtime pitch shifter and time compressor/expander), but that's a significant undertaking. There are no Python bindings for libsoundtouch, so using it would mean mucking with SWIG, which has always given me fits. On Linux at least, there is an alternative solution that ultimately provides more flexibility anyway in building a sound layer that permits all sorts of cool sound effect possibilities. This HOWTO attempts to document how the whole thing fits together, how to implement it on your own system, and how to use it in production at a karaoke (or really any DJ'ed) show. 1. The Architecture. The system we'll be building uses JACK to connect different sound applications together and to the machine's sound card. PyKaraoke will provide the CD+G audio source that we'll be applying pitch-shifting effects to. XMMS will provide filler audio in this example, simply because it has a JACK output driver and is easy to work with. It also has a high-quality crossfader plugin that produces outstanding audio results. JACK Rack, with Tom's Audio Processing LADSPA plugins providing pitch-shifting. As an added bonus, I'll demonstrate how to get MPlayer into the mix as well, to provide multimedia clips at shows where a television or projector is available. 1.1 JACK http://jackit.sourceforge.net/ The JACK Audio Connection Kit is a real-time virtual mixing board for Linux (and possibly other platforms; I haven't yet investigated this) that uses a low-latency server and protocol to connect sound applications and devices to each other. It can control all sorts of real hardware (sound cards, MIDI controllers, etc.) and can accept inputs from just about anything (media players, MIDI controllers, etc.) for both audio and control. It can make use of a stock Linux kernel, or one that has been configured with preempting and real-time features to ensure no pops or gaps in audio playback even when many different tools are in active use on the chain. JACK includes a useful tool, qjackctl, that will be used in this HOWTO to configure JACK and to automate patching our different tools together. 1.2 JACK Rack http://jack-rack.sourceforge.net/ JACK Rack is a sound processor designed for use with JACK exclusively; it presents a configurable number of "default" channels to JACK and can load effects modules (like "echo," "pitch shift," "reverb," etc.) in any order. Sound flows through the modules top-to-bottom as they're shown in the interface. Modules can be enabled or disabled (when disabled, they do nothing to the sound; it simply flows through them to the next module), and moved up and down in the stack. This HOWTO uses JACK Rack for two things: first, it is used to perform the actual pitch-shifting work when needed (audio from PyKaraoke is passed to JACK Rack instead of straight ot the sound card). Second, it performs crossfading work; I use different audio sources (specifically, XMMS and MPlayer) during my shows, and smoothly transitioning from them to CD+G music and back is important. JACK Rack is, in this configuration, the only piece of software on the chain that is connected to the sound card. All audio playback runs through JACK Rack whether it is doing anything to the sound or not. 1.3 XMMS http://www.xmms.org/ XMMS is a multimedia player for Linux. It is an older piece of software (not actively maintained anymore; its developers are focusing on a new 2.0 release), but assuming it'll start up and run on your system, it's very reliable and useful for this purpose. It supports MP3, Ogg Vorbis, WAV, FLAC, and all sorts of other audio formats. It can play video (via MPlayer, actually), but we want manual control over that kind of thing so we'll only be using XMMS for audio. XMMS' plugin system means we can get automated crossfading between songs XMMS plays *and* connect the whole thing to JACK as just another audio source. 1.4 MPlayer http://www.mplayerhq.hu/ MPlayer is a multimedia player for Linux. It supports audio and video playback, tons of media formats, lots of output devices and types, and has more features than I can adequately count here. For our purposes, we'll simply be chaining it to JACK as an audio source (letting it do its own thing for video, if needed) so we can crossfade between it and the filler music XMMS provides. 1.5 Tom's Audio Processing LADSPA Plugins http://tap-plugins.sourceforge.net/ This set of plugins, compatible with JACK Rack, includes the one we want: pitch shifting. This is what will provide us with digital pitch-shifting for CD+G playback. Really, it can affect all sound, but we just want it to affect CD+G. 2. Setting Up the Parts It's beyond the scope of this HOWTO to document the installation/configuration procedure for the software used; if you're using a modern Linux distribution (like Debian, Ubuntu, or Gentoo), its package management system should already have these packages available. JACK is theoretically the "trickiest" part to get working, but it's actually pretty forgiving. Once you can run qjackctl and play some kind of sound through it, you're good to go. You oddly enough don't need an MPlayer build with native JACK support; you can "trick" it with ALSA and SDL, as that's what we're doing with PyKaraoke as well. If your MPlayer has native JACK support, great; if not, try running it with SDL audio output. If that works, you're still golden. XMMS needs the JACK output plugin, available at the XMMS homepage. PyKaraoke requires no modifications for this process to work. JACK Rack should "just work" once it's compiled and you run it. 2.1. Configuring ALSA to Talk to JACK By default, ALSA just talks to your real sound device. We want it to default to connecting to JACK instead, though, so it's necessary to create a .asoundrc file. It belongs in the home directory of the account you're using for production shows. Just edit ~/.asoundrc and you should be fine. Its contents should be: pcm.!default { type plug slave { pcm "jack" } } pcm.jack { type jack playback_ports { 0 alsa_pcm:playback_1 1 alsa_pcm:playback_2 } capture_ports { 0 alsa_pcm:capture_1 1 alsa_pcm:capture_2 } } Test that this is working properly by starting JACK (run qjackctl and start a JACK server), then watch the "Connections" bay as you run "aplay somefile.mp3" -- you should see a new client appear, and it will probably automatically connect to the sound card (this is JACK's default behavior). 2.2. Setting Up the Sound Processor (JACK Rack) Start up JACK Rack (the command is "jack-rack"). It will start with an empty effects stack, which is what we want. Add the first effect we want: the pitch-shifter. It's called "TAP Pitch-Shifter". Then, add the second effect we're after: the crossfader. It's called "Crossfader." Save the stack to a file you'll keep handy (you can just open this stack later as a preset instead of having to set it up every time). Disable both plugins for now; we want to get sound flowing first before we start changing it. 2.3. Setting Up XMMS Switch XMMS' output driver to the Crossfader plugin, then in the Crossfader configuration, select the JACK output driver as the desired output driver. Start XMMS playing; you should immediately see it appear as a client in the qjackctl Connections window. Again, it should automatically connect to the sound card by default. This isn't what we want, by the way, but it's how things start out. 2.4. Setting Up MPlayer and PyKaraoke PyKaraoke needs no modifications because it uses SDL, which honors .asoundrc. MPlayer needs to be told either to use JACK or SDL as its audio output method: # mplayer -ao sdl ... -or- # mplayer -ao jack ... Fire off an MPlayer instance with a song to make sure it appears as a client in the qjackctl Connections window. If you're using MPlayer with SDL, you'll notice that PyKaraoke and MPlayer appear pretty much the same within the Connections window. That's an important detail later. 3. Putting It All Together With all the pieces now talking to JACK, and JACK talking to the sound card, it's time to build a Patchbay configuration to automate routing of sound to the appropriate tools and devices. Here's how it will work when it's all set up: * XMMS will feed directly to the Crossfader plugin's connectors in JACK Rack. * MPlayer and PyKaraoke will feed to JACK Rack's main connectors. * JACK Rack will connect directly (and exclusively) to the sound card. Open the Patchbay window in qjackctl. We'll start with the input devices. Make sure JACK Rack is running, by the way. That makes life much easier. 3.1. Adding Input Sockets Select "Add" in the Input Sockets column to create a new input socket. Name it "Sound Card." From the Client dropdown, select "alsa_pcm" (or whatever name is assigned to your real sound device). "playback_1" should appear in the Plug dropdown; click "Add Plug" to add it. "playback_2" should appear there next; click "Add Plug" to add that, too. Every Input Socket we're creating will handle stereo sound. We need this socket to be exclusive, so check the "Exclusive" box. Hit "OK" to add the socket. Add the next Input Socket: name it "Processed Sound." This time, select "jack_rack_[0-9]+" from the Client dropdown. Assuming you've got the crossfade plugin installed in your stack in JACK Rack, if you look at the Plug dropdown, you'll see *two* pairs of plugs, not one; this is because the crossfader adds its own stereo channel to JACK Rack's inputs. Add the "in_1" and "in_2" plugs to this socket, but DON'T add the crossfader plugs. Hit "OK" to add the socket. Add one last Input Socket: name it "Unprocessed Sound." Select "jack_rack_[0-9]+" again from the Client dropdown, and *this* time, add the crossfader plugs to the socket. Click "OK" to add the socket. 3.2. Adding Output Sockets It's easier to set the output sockets up while the different media players are running, because qjackctl automatically generates a regular expression to match them for you when it sees them running. JACK Rack is already running, so we'll set that output socket up first. Click "Add" next to the Output Sockets column. Name it "Sound Processor." Select "jack_rack_[0-9]+" from the Client dropdown, then add both output plugs to the Socket. Save the socket with "OK." Next, start up XMMS, start it playing (through JACK), and click "Add" again to add a new Output Socket. Name it "Filler." There should be an XMMS-related selection in the Client dropdown; select it, add its two output plugs, and save the socket with "OK." Finally, start a PyKaraoke instance (just have it play a CD+G song). Click "Add" again to add the last Output Socket. Name it "Karaoke" (or something similar). You should now see an "alsaP\.[0-9]+\.1" or similar entry in the Client list; this is how SDL clients appear to JACK. Select it, and add its two plugs. 3.3. Connect It All Together Now comes the fun part -- teaching JACK to automatically connect things to the right places. First, disconnect everything. Go to the Connections panel in qjackctl and select Disconnect All. It will ask for confirmation; give it. The Patchbay lets us specify *automatic* connections; that is, when a client connects, JACK will check against the active Patchbay profile and if the client matches some part of the configuration, JACK will automatically connect it where it needs to go. In the Output Sockets column, click on the "Sound Processor" socket you created. In the Input Sockets column, click the "Sound Device" socket you created. Click "Connect" to connect them. Remember that we set the sound device to be exclusive, so this will be the only connection JACK will permit to the sound card. This prevents other clients from automatically stealing the card directly. Next, in Output Sockets, click "Filler," then in Input Sockets, click on the "Unprocessed Sound" socket, and then click "Connect." This connects XMMS directly to the crossfader in JACK Rack; remember that sound flows top-down through the stack in JACK Rack, but this sound is entering the rack *at* the crossfader. This means that no matter what you do with the pitch-shifting plugin, your filler music won't be pitch-shifted. In fact, any effect you apply to sounds before the crossfade plugin won't affect the filler music. The crossfade module can fade between this filler sound and the main inputs, where we'll be feeding multimedia and CD+G output. Finally, in Output Sockets, click "Karaoke," then in Input Sockets, click "Processed Sound." Then click "Connect." This connects all SDL-based clients to JACK Rack's main inputs, which get passed through all the filters in the chain. Save the Patchbay configuration, and then Activate it. If all has gone well, you're done. Play a CD+G file with PyKaraoke and watch the Connection panel -- it should appear and be automatically connected. Start XMMS playing and it should be automatically connected to the crossfader. To play around with pitch-shifting, make sure to activate the module in JACK Rack by clicking the "Enable" button. The crossfader needs to be enabled, too, so do that as well. Play around with it -- you've got a digital pitch-shifter and crossfader! 4. Conclusion There are still ways to improve this; my next goal is to get my hands on a MIDI controller that gives me a physical slider to use to control the crossfader instead of using the one shown in JACK Rack's window. It does work pretty well, though; I've used this now for three karaoke shows (5 hours each) and have not had any performance difficulties with it. Feel free to contact me (at [EMAIL PROTECTED]) if you have questions about this. I've posted this HOWTO at http://willfe.com/index.php/Pitch-shifting_With_PyKaraoke_and_JACK_HOWTO as well. I'll get it formatted properly here in a few minutes. -- Looking for something to read? Visit http://willfe.com/ ... it's easy, safe, and fun for the whole family! ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid0944&bid$1720&dat1642 _______________________________________________ Pykaraoke-discuss mailing list Pykaraoke-discuss@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/pykaraoke-discuss
