Pitch shifting for Linux transcribers.

Pitch shifting a podcast to slow it down while keeping voices in an audible range is something that is embedded in certain applications for Windows users. If you are a Linux user, though, how do you go about it?

Well, there are multiple options, but I've found the best is to use libasound LADSPA plugins -- a set of sound tools used by people who do pro audio recording under Linux. Using a LADSPA plugins you can play a sound pitch-shifted with whatever player -- even video players -- you use for transcription, as long as it has a libasound (a.k.a. "alsa") output driver.

For example, the alsaplayer application has a speed control and also has a daemon mode that can be tied to various input devices like foot pedals, so combined with LADSPA plugins, it's all you really need. Setup is very simple on any modern Linux system (where libasound is usually already installed by default.)

First you need to find and install the LADSPA plugins. The ones you need are "Tom's Audio Processing LADSPA plugins" -- look for a "tap-plugins" package with your package manager, or you can go to tap-plugins.sourceforge.net to find packages for other distributions.

Once you have those installed, all you need to do is place the following text in your ~/.asoundrc file:

pcm.transcribe { type ladspa slave.pcm "plughw:0,0"; path "/usr/lib/ladspa"; plugins [ { label tap_pitch input { controls [12 100 -90 0] } }]}


You may have to change the path "/usr/lib/ladspa" if your distribution puts the plugins someplace weird.

Now just run alsaplayer with an extra command switch: alsaplayer -dplug:transcribe ...and anything you play with that alsaplayer will sound like Alvin and The Chipmunks. The plugin even allows you to mix in some of the original audio -- just change that -90 to a number closer to zero, and you'll hear a mix of the pitch-shifted audio with the original audio. This can help consonants sound a bit better.

Documentation for the other controls can be found here: tap-plugins.sourceforge.net/ladspa/pitch.html I don't know how many turkers use Linux, but if there is enough interest, I can show you how to use external controls like joysticks as footpedals to control alsaplayer in a future post.

Posted by skids

Comments

[MDG]

Hi! Sorry for posting to the wrong entry below - ooops!
I would love more info about using a joystick to control alsaplayer - anything regarding linux. I do medical transcription currently.

Skids, would love to chat with you.

Thanks!
MDG