Category Archives: Speech Tools

Google Speech API – Full Duplex PHP Version

So this is a follow up to my post a while ago, talking about how to use the Google Speech Recognition API built in to Google Chrome.

Since my last post, Chrome has had some significant upgrades to this feature- specifically around the length of audio you can pass to the API. The old version would only let you pass very short clips (only a few seconds), but the new API is a full-duplex streaming API. What this means, is that it actually uses two HTTP connections- one POST request to upload the content as a “live” chunked stream, and a second GET request to access the results, which makes much more sense for longer audio samples, or for streaming audio.

I created a simple PHP class to access this API; while this likely won’t make sense for anybody that wants to do a real-time stream, it should satisfy most cases where people just want to send “longer” audio clips.

Before you can use this PHP class, you must get a developer API key from Google. The class does not include one, and I cannot give you one- they’re free, and easy to get just go to the Google APIs site, and sign up for one.


Then download the class below, and start with a simple example:

require 'google_speech.php';

$s = new cgoogle_speech('put your API key here'); 

$output = $s->process('@test.flac', 'en-US', 8000);      


Audio can be passed as a filename (by prefixing the ‘@’ sign in front of the file name), or by passing in raw FLAC content. The second argument is an IETF language tag. I’ve only been able to test with both English and French, but I assume others work. It defaults to ‘en-US’. The third argument is sample rate, it defaults to 8000.

** Your sample rate must match your file- if it doesn’t, you’ll either get nothing returned, or you’ll get a really bad transcription. **

The output will return as an array, and should look something like this:

    [0] => Array
            [alternative] => Array
                    [0] => Array
                            [transcript] => my CPU is a neural net processor a learning computer
                            [confidence] => 0.74177068
                    [1] => Array
                            [transcript] => my CPU is the neuron that process of learning
                    [2] => Array
                            [transcript] => my CPU is the neural net processor a learning
                    [3] => Array
                            [transcript] => my CPU is the neuron that process a balloon
                    [4] => Array
                            [transcript] => my CPU is the neural net processor a living
            [final] => 1

Get the PHP class here:

PERL Text-to-Speech using Cepstral voices (libswift)

I’ve released two new PERL modules:

Speech::Swift – a PERL interface to the Cepstral text-to-speech engine, Swift.


Speech::Swift::Simple – a simplified interface to Speech::Swift

The libswift shared library is required to support this code, which is included with every voice downloaded from Cepstral.

The reason for two releases, is that the Speech::Swift module exports all (well, almost all) the underlying functions of the library, while Speech::Swift::Simple has a simplified interface to generate speech in a just a few function calls.

For example:


use Speech::Swift::Simple;

# create a new Speech::Swift::Simple with one channel audio, and 16bit encoding.
my $s = new Speech::Swift::Simple(
         channels => 1,
         encoding => Speech::Swift::AUDIO_ENCODING_PCM16

# set the voice to use by name

# synthesize the text, and return it as a Speech::Swift::Simple::Wav object
my $wav = $s->generate("My name is allison");

# write the wav object to a file.

Or use the Speech::Swift library directly, for a more low-level interface.

The audio output is always as a WAV file; you can use one of the many audio modules available from CPAN, like Audio::GSM or Audio::MPEG, to re-encode the audio as needed.

Both PERL modules are available for download from CPAN now.

First Release of PHP Swift TTS Extension

I’m happy to announce the first release of the Swift Text-To-Speech PHP extension; the swift engine is the free TTS engine provided with any Cepstral TTS voice. A lot of Asterisk fans out there will recognize the Cepstral Allison voice, as the default voice for Asterisk installations.

The extension will only work on systems support by the Swift engine, and has only been tested (so far) on Linux (CentOS).

The extension will generate audio based on the text provided, and can be exported in several different audio formats, including:

  • PCM (RAW audio)
  • u-law / a-law (logarithmically encoded RAW audio)
  • WAV (RAW audio)
  • GSM (when compiled with the libgsm library)
  • MP3 (when compiled with the libmp3lame library)

A simple example on how to use this:

// create the new TTS object
$tts = new SwiftTTS();

// set a voice to use for generation

// generate text, and return a stream for the audio
$s = $tts->generate("hello my name is allison", SwiftTTS::FORMAT_WAV);
if ($s !== false)
        // write the stream contents to a file
        file_put_contents("audio.wav", $s);

For more details, and to download the current version, see the Google Code page.

Accessing Google Speech API / Chrome 11

I’ve posted an updated version of this article here, using the new full-duplex streaming API.

Just yesterday, Google pushed version 11 of their Chrome browser into beta, and along with it, one really interesting new feature- support for the HTML5 speech input API. This means that you’ll be able to talk to your computer, and Chrome will be able to interpret it. This feature has been available for awhile on Android devices, so many of you will already be used to it, and welcome the new feature.

If you’re running Chrome version 11, you can test out the new speech capabilities by going to their simple test page on the site:

Genius! but how does it work? I started digging around in the Chromium source code, to find out if the speech recognition is implemented as a library built into Chrome, or, if it sends the audio back to Google to process- I know I’ve seen the Sphynx libraries in the Android build, but I was sure the latter was the case- the speech recognition was really good, and that’s really hard to do without really good language models- not something you’d be able to build into a browser.

I found the files I was looking for in the chromium source repo:

It looks like the audio is collected from the mic, and then passed via an HTTPS POST to a Google web service, which responds with a JSON object with the results. Looking through their audio encoder code, it looks like the audio can be either FLAC or Speex– but it looks like it’s some sort of specially modified version of Speex- I’m not sure what it is, but it just didn’t look quite right.

If that’s the case, there should be no reason why I can’t just POST something to it myself?

The URL listed in is:

So a quick few lines of PERL (or PHP or just use wget on the command line):


require LWP::UserAgent;

my $url = "";
my $audio = "";

open(FILE, "<" . $ARGV[0]);
    $audio .= $_;

my $ua = LWP::UserAgent->new;

my $response = $ua->post($url, Content_Type => "audio/x-flac; rate=16000", Content => $audio);
if ($response->is_success)
    print $response->content;


This quick PERL script uses LWP::UserAgent to POST the binary audio from my audio clip; I recorded a quick wav file, and then converted it to FLAC on the command line (see SoX for more info)

To run it, just do:

[root@prague mike]# ./speech i_like_pickles.flac

The response is pretty straight forward JSON:

    "status": 0,
    "id": "b3447b5d98c5653e0067f35b32c0a8ca-1",
    "hypotheses": [
        "utterance": "i like pickles",
        "confidence": 0.9012539
        "utterance": "i like pickle"

I’m not sure if Google is intending this to be a public, usable web service API, but it works- and has all sorts of possibilities!