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23 Audio output

If you have never heard any audio ever on your machine then you must first work out if you have the appropriate hardware. If you do, you also need the appropriate software to drive it. Festival can directly interface with a number of audio systems or use external methods for playing audio.

The currently supported audio methods are

‘NAS’
NCD's NAS, is a network transparent audio system (formerly called netaudio). If you already run servers on your machines you simply need to ensure your AUDIOSERVER environment variable is set (or your DISPLAY variable if your audio output device is the same as your X Windows display). You may set NAS as your audio output method by the command 
          (Parameter.set 'Audio_Method 'netaudio)


‘/dev/audio’
On many systems /dev/audio offers a simple low level method for audio output. It is limited to mu-law encoding at 8KHz. Some implementations of /dev/audio allow other sample rates and sample types but as that is non-standard this method only uses the common format. Typical systems that offer these are Suns, Linux and FreeBSD machines. You may set direct /dev/audio access as your audio method by the command 
          (Parameter.set 'Audio_Method 'sunaudio)


‘/dev/audio (16bit)’
Later Sun Microsystems workstations support 16 bit linear audio at various sample rates. Support for this form of audio output is supported. It is a compile time option (as it requires include files that only exist on Sun machines. If your installation supports it (check the members of the list *modules*) you can select 16 bit audio output on Suns by the command 
          (Parameter.set 'Audio_Method 'sun16audio)

Note this will send it to the local machine where the festival binary is running, this might not be the one you are sitting next to—that's why we recommend netaudio. A hacky solution to playing audio on a local machine from a remote machine without using netaudio is described in Installation

‘/dev/dsp (voxware)’
Both FreeBSD and Linux have a very similar audio interface through /dev/dsp. There is compile time support for these in the speech tools and when compiled with that option Festival may utilise it. Check the value of the variable *modules* to see which audio devices are directly supported. On FreeBSD, if supported, you may select local 16 bit linear audio by the command 
          (Parameter.set 'Audio_Method 'freebsd16audio)

While under Linux, if supported, you may use the command 

          (Parameter.set 'Audio_Method 'linux16audio)

Some earlier (and smaller machines) only have 8bit audio even though they include a /dev/dsp (Soundblaster PRO for example). This was not dealt with properly in earlier versions of the system but now the support automatically checks to see the sample width supported and uses it accordingly. 8 bit at higher frequencies than 8K sounds better than straight 8k ulaw so this feature is useful.


‘mplayer’
Under Windows NT or 95 you can use the mplayer command which we have found requires special treatement to get its parameters right. Rather than using Audio_Command you can select this on Windows machine with the following command 
          (Parameter.set 'Audio_Method 'mplayeraudio)

Alternatively built-in audio output is available with 

          (Parameter.set 'Audio_Method 'win32audio)


‘SGI IRIX’
Builtin audio output is now available for SGI's IRIX 6.2 using the command 
          (Parameter.set 'Audio_Method 'irixaudio)


‘Audio Command’
Alternatively the user can provide a command that can play an audio file. Festival will execute that command in an environment where the shell variables SR is set to the sample rate (in Hz) and FILE which, by default, is the name of an unheadered raw, 16bit file containing the synthesized waveform in the byte order of the machine Festival is running on. You can specify your audio play command and that you wish Festival to execute that command through the following command 
          (Parameter.set 'Audio_Command "sun16play -f $SR $FILE")
          (Parameter.set 'Audio_Method 'Audio_Command)

On SGI machines under IRIX the equivalent would be 

          (Parameter.set 'Audio_Command
                     "sfplay -i integer 16 2scomp rate $SR end $FILE")
          (Parameter.set 'Audio_Method 'Audio_Command)
The Audio_Command method of playing waveforms Festival supports two additional audio parameters. Audio_Required_Rate allows you to use Festival's internal sample rate conversion function to any desired rate. Note this may not be as good as playing the waveform at the sample rate it is originally created in, but as some hardware devices are restrictive in what sample rates they support, or have naive resample functions this could be optimal. The second additional audio parameter is Audio_Required_Format which can be used to specify the desired output forms of the file. The default is unheadered raw, but this may be any of the values supported by the speech tools (including nist, esps, snd, riff, aiff, audlab, raw and, if you really want it, ascii). For example suppose you have a program that only plays sun headered files at 16000 KHz you can set up audio output as 
     (Parameter.set 'Audio_Method 'Audio_Command)
     (Parameter.set 'Audio_Required_Rate 16000)
     (Parameter.set 'Audio_Required_Format 'snd)
     (Parameter.set 'Audio_Command "sunplay $FILE")

Where the audio method supports it, you can specify an alternative audio device for machines that have more than one audio device. 

     (Parameter.set 'Audio_Device "/dev/dsp2")

If Netaudio is not available and you need to play audio on a machine different from teh one Festival is running on we have had reports that snack (http://www.speech.kth.se/snack/) is a possible solution. It allows remote play but importnatly also supports Windows 95/NT based clients.

Because you do not want to wait for a whole file to be synthesized before you can play it, Festival also offers an audio spooler that allows the playing of audio files while continuing to synthesize the following utterances. On reasonable workstations this allows the breaks between utterances to be as short as your hardware allows them to be.

The audio spooler may be started by selecting asynchronous mode 

     (audio_mode 'async)

This is switched on by default be the function tts. You may put Festival back into synchronous mode (i.e. the utt.play command will wait until the audio has finished playing before returning). by the command 

     (audio_mode 'sync)

Additional related commands are

(audio_mode 'close)
Close the audio server down but wait until it is cleared. This is useful in scripts etc. when you wish to only exit when all audio is complete.
(audio_mode 'shutup)
Close the audio down now, stopping the current file being played and any in the queue. Note that this may take some time to take effect depending on which audio method you use. Sometimes there can be 100s of milliseconds of audio in the device itself which cannot be stopped.
(audio_mode 'query)
Lists the size of each waveform currently in the queue.