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Article Written By:
Johann Dowa

Open Source: OpenEars Speech Recognition And Text-To-Speech Library Undergoes Significant Updates


At the start of this year, I mentioned an open source speech recognition, and text-to-speech library.  At that time it was already a great library, used in several apps, but recently it has undergone a significant update.

This new update is extremely significant and improving upon everything within the library providing greater performance, and speech recognition accuracy along with the documentation being re-written for Xcode 4.

Here’s a list of what the latest version can do (taken from the official website):

OpenEars .91 can:

  • Listen continuously for speech on a background thread, while suspending or resuming speech processing on demand, all while using less than 8% CPU on average on a first-generation iPhone (decoding speech, text-to-speech, updating the UI and other intermittent functions use more CPU),
  • Use any of 8 voices for speech and switch between them on the fly,
  • Know whether headphones are plugged in and continue voice recognition during text-to-speech only when they are plugged in,
  • Support bluetooth audio devices (very experimental in this version),
  • Dispatch information to any part of your app about the results of speech recognition and speech, or changes in the state of the audio session (such as an incoming phone call or headphones being plugged in),
  • Deliver level metering for both speech input and speech output so you can design visual feedback for both states.
  • Support JSGF grammars,
  • Dynamically generate new ARPA language models in-app based on input from an NSArray of NSStrings,
  • Switch between ARPA language models on the fly,
  • Be easily interacted with via standard and simple Objective-C methods,
  • Control all audio functions with text-to-speech and speech recognition in memory instead of writing audio files to disk and then reading them,
  • Drive speech recognition with a low-latency Audio Unit driver for highest responsiveness,
  • Be installed in a Cocoa-standard fashion using static library projects that, after initial configuration, allow you to target or re-target any SDKs or architectures that are supported by the libraries (verified as going back to SDK 3.1.2 at least) by making changes to your main project only.

You can find the official website here:

You can find the download in the getting started tutorial here:

If you’ve wanted to add speech recognition into an app without having to license a costly API then you will want to check it out.


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