Open Source Speech Recognition

I’m currently working on the Vaani project at Mozilla, and part of my work on that allows me to do some exploration around the topic of speech recognition and speech assistants. After looking at some of the commercial offerings available, I thought that if we were going to do some kind of add-on API, we’d be best off aping the Amazon Alexa skills JS API. Amazon Echo appears to be doing quite well and people have written a number of skills with their API. There isn’t really any alternative right now, but I actually happen to think their API is quite well thought out and concise, and maps well to the sort of data structures you need to do reliable speech recognition.

So skipping forward a bit, I decided to prototype with Node.js and some existing open source projects to implement an offline version of the Alexa skills JS API. Today it’s gotten to the point where it’s actually usable (for certain values of usable) and I’ve just spent the last 5 minutes asking it to tell me Knock-Knock jokes, so rather than waste any more time on that, I thought I’d write this about it instead. If you want to try it out, check out this repository and run npm install in the usual way. You’ll need pocketsphinx installed for that to succeed (install sphinxbase and pocketsphinx from github), and you’ll need espeak installed and some skills for it to do anything interesting, so check out the Alexa sample skills and sym-link the ‘samples‘ directory as a directory called ‘skills‘ in your ferris checkout directory. After that, just run the included example file with node and talk to it via your default recording device (hint: say ‘launch wise guy‘).

Hopefully someone else finds this useful – I’ll be using this as a base to prototype further voice experiments, and I’ll likely be extending the Alexa API further in non-standard ways. What was quite neat about all this was just how easy it all was. The Alexa API is extremely well documented, Node.js is also extremely well documented and just as easy to use, and there are tons of libraries (of varying quality…) to do what you need to do. The only real stumbling block was pocketsphinx’s lack of documentation (there’s no documentation at all for the Node bindings and the C API documentation is pretty sparse, to say the least), but thankfully other members of my team are much more familiar with this codebase than I am and I could lean on them for support.

I’m reasonably impressed with the state of lightweight open source voice recognition. This is easily good enough to be useful if you can limit the scope of what you need to recognise, and I find the Alexa API is a great way of doing that. I’d be interested to know how close the internal implementation is to how I’ve gone about it if anyone has that insider knowledge.

Mozillian and GNOME Foundation member, hacks on Firefox for Android, formerly of Intel and OpenedHand.

Mail me at <contact> at <domain>.
View all posts by Chris Lord


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