This section describe the I/O configuration system of jMax Phoenix. The configuration of jMax Phoenix is quite different than the original jMax. It is based on XML files instead of tcl scripts, and adopt a quite simpler, yet powerfull, model.

I/O configurations are described in the XML configuration file, using an io-configuration tag. Multiple configuration can be described. Each of them have a unique name.

An I/O configuration is a list of device descriptions and of mapping commands, mapping device names to the names used for i/o within a patch.

A specific i/o configuration is selected and installed by specifying it in the preferences section of the configuration file (site or user).

The following XML excerpt is an example of configuration for portaudio devices.

<jmax>
  .......
  <io-configuration name="portaudio">
 
    <device name="portAudioStereoOut"
	    type="portdev_dac"
	    deviceName="portaudio_default"
	    out_channels="2"/>
 
    <map>
      <logical-device type="out~" name="main"/>
      <device name="portAudioStereoOut" />
    </map>
  </io-configuration>
  ......
</jmax>

The io-configuration element can include a number of device elements and a number of map elements.

The device element declare a jMax device to be used by this configuration. A jMax device is an abstraction of an actual device or library to access audio or midi devices. It is a way for jMax to adapt to the different choices available on the different platforms.

Currently, jMax support I/O thru the portaudio/portmidi library (that can map to ALSA, Jack in some case, and OSS), and a native OSS interface. The source tree include also old interfaces for SGI and Solaris audio interfaces, that may be resurrected once a version for these platforms will be made available.

The device element have a name attribute, that is used to identify the device in the map element, a type attribute that identify the actual device type to use (portaudio audio output, in this case), and a number of attributes that depends on the device itself, typically including at least the number of channels and other configuration parameter for the device. You'll find a detailed list of supported devices for all the platforms and their parameters here.

The map element declare a mapping from a name or port number used in the patch objects (in the in~ and out~ objects for audio, or in midi input/output objects) and the declared devices. This level of indirections allows to write patches that do not depends on a specific machine configuration, but that can be run on any machine by just adapting the configuration, without editing the patch itself.

The first audio device mapped is also associated to the dac~ or adc~ object, objects that do not take the device name argument. As long as the audio library used support it, jMax can use multiple audio and midi devices.

The map element need two subelement, logical-device and device. logical-device specify which device name (and of which kind) we are mapping to the device identified by the device element. logical-device take a type attribute, that currently can be:

• in~ for audio input devices
• out~ for audio output devices
• midi for midi devices

in~ and out~ logical devices have a name attribute, that is the name of the device used in the corresponding objects, while midi logical devices have a port attribute, that is the midi port number mapped to the specified device. The device tag specify the device by name, and have a single device attribute.

Please note that since the mapping is at the device, and not channel, level, it is a lot less useful than expected. The objective is to be able to write a patch using a ideal input/output configuration (for example Stereo PA output, 4 mono stage return, stereo recording output) using symbolic name for each input/output connection, and then to map these logical inputs and outputs to existing audio interfaces (for example, to channels 1 .. 8 or your Motu or Focusrite interface).

This is not possible today, because the mapping is done at the whole device level. We plan to introduce this feature later, as a consequence of a new DSP compiling strategy (so, no, do not expect it in a few weeks).

Once defined, a specific i/o configuration is selected and installed by specifying something like:

<jmax>
  .....
  <preferences>
    ....
    <io-configuration name="portaudio"/>
    ....
  </preferences>
  .....
</jmax>

in the user configuration file.

The jMax distributions contains a small number of ready to use configurations, defined in the jmax/config/jmax.xml file, that can be used as they are or copied and modified as needed.

The defined configurations are documented here .

Using the preferences in a configuration file (either the site jmax.xml file or the personal configuration file at ~/.jmax.xml) you can set the basic DSP parameters, i.e. the sampling frequency used in DSP, the computation vector size (in the original jMax was fixed at 64, in jMax Phoenix can be any 2 power between 32 and 2048), and the default output fifo length.

The syntax to be used is the following :

<jmax>
  <preferences>
    ....
    <fts>
      <param name="sampling_rate" type="int" value="44100"/>
      <param name="vector_size"  type="int" value="256"/>
      <param name="fifo_size"    type="int" value="256"/>
    </fts>
    ....
  </preferences>
</jmax>

Declaring the above in the personal configuration file ( ~/.jmax.xml ) will overwrite the default parameter value defined in the installation configuration file.