Sound init routines

Allegro allows you to use the sound hardware in two ways: automatic, or manual. Usually you should try the automatic version first. This means calling install_sound() with the autodetection parameters and using the rest of the sound functions to play samples or music. In this situation, Allegro will handle the sound devices and mix the samples and/or music the best way it can.

However, sound hardware has a limitation on the number of samples it may play all at the same time (from now on, called hardware voices). When you exceed this limit, Allegro will cut off one of the samples being played and reproduce the new one. Depending on the type of sounds you are playing, how many of them you need at the same time and their nature (e.g: vital audio feedback to the user or useless "ping" when some shrapnel hits a rock in the scenery) you will want to specify more carefully how hardware voices are reserved and which samples have priority over others.

The hardware voice reservation phase has to be done before the call to install_sound(), since it directly affects how Allegro talks to the sound drivers.


int detect_digi_driver(int driver_id);

Detects whether the specified digital sound device is available. This function must be called _before_ install_sound().

Return value: Returns the maximum number of voices that the driver can provide, or zero if the hardware is not present.

See also: install_sound, reserve_voices, DIGI_*/DOS, DIGI_*/Windows, DIGI_*/Unix, DIGI_*/BeOS, DIGI_*/QNX, DIGI_*/MacOSX.
int detect_midi_driver(int driver_id);

Detects whether the specified MIDI sound device is available. This function must be called _before_ install_sound().

Return value: Returns the maximum number of voices that the driver can provide, or zero if the hardware is not present.

There are two special-case return values that you should watch out for: if this function returns -1 it is a note-stealing driver (eg. DIGMID) that shares voices with the current digital sound driver, and if it returns 0xFFFF it is an external device like an MPU-401 where there is no way to determine how many voices are available.

See also: install_sound, reserve_voices, MIDI_*/DOS, MIDI_*/Windows, MIDI_*/Unix, MIDI_*/BeOS, MIDI_*/QNX, MIDI_*/MacOSX.
void reserve_voices(int digi_voices, int midi_voices);

Call this function to specify the number of voices that are to be used by the digital and MIDI sound drivers respectively. This must be done _before_ calling install_sound(). If you reserve too many voices, subsequent calls to install_sound() will fail. How many voices are available depends on the driver, and in some cases you will actually get more than you reserve (eg. the FM synth drivers will always provide 9 voices on an OPL2 and 18 on an OPL3, and the SB digital driver will round the number of voices up to the nearest power of two). Pass negative values to restore the default settings. You should be aware that the sound quality is usually inversely related to how many voices you use, so don't reserve any more than you really need.
See also: set_volume_per_voice, install_sound, detect_digi_driver, detect_midi_driver, get_mixer_voices.
void set_volume_per_voice(int scale);

By default, Allegro will play a centered sample at half volume on both the left and right channel. A sample panned to the far right or left will be played at maximum volume on that channel only. This is done so you can play a single panned sample without distortion. If you play multiple samples at full volume, the mixing process can result in clipping, a noticeable form of distortion. The more samples, the more likely clipping is to occur, and the more clipping, the worse the output will sound.

If clipping is a problem - or if the output is too quiet - this function can be used to adjust the volume of each voice. You should first check that your speakers are at a reasonable volume, Allegro's global volume is at maximum (see set_volume() below), and any other mixers such as the Windows Volume Control are set reasonably. Once you are sure that Allegro's output level is unsuitable for your application, use this function to adjust it.

Each time you increase the parameter by one, the volume of each voice will halve. For example, if you pass 4, you can play up to 16 centred samples at maximum volume without distortion.

If you pass 0 to this function, each centred sample will play at the maximum volume possible without distortion, as will all samples played through a mono driver. Samples at the extreme left and right will distort if played at full volume. If you wish to play panned samples at full volume without distortion, you should pass 1 to this function. Note: this is different from the function's behaviour in WIPs 3.9.34, 3.9.35 and 3.9.36. If you used this function under one of these WIPs, you will have to increase your parameter by one to get the same volume.

Note: The default behaviour has changed as of Allegro 4.1.15. If you would like the behaviour of earlier versions of Allegro, pass -1 to this function. Allegro will choose a value dependent on the number of voices, so that if you reserve n voices, you can play up to n/2 normalised samples with centre panning without risking distortion. The exception is when you have fewer than 8 voices, where the volume remains the same as for 8 voices. Here are the values, dependent on the number of voices: 

     1-8 voices - set_volume_per_voice(2)
      16 voices - set_volume_per_voice(3)
      32 voices - set_volume_per_voice(4)
      64 voices - set_volume_per_voice(5)
Of course this function does not override the volume you specify with play_sample() or voice_set_volume(). It simply alters the overall output of the program. If you play samples at lower volumes, or if they are not normalised, then you can play more of them without distortion.

It is recommended that you hard-code the parameter into your program, rather than offering it to the user. The user can alter the volume with the configuration file instead, or you can provide for this with set_volume().

To restore volume per voice to its default behaviour, pass 1.

See also: reserve_voices, set_volume, install_sound, detect_digi_driver, detect_midi_driver.
int install_sound(int digi, int midi, const char *cfg_path);

Initialises the sound module. You should normally pass DIGI_AUTODETECT and MIDI_AUTODETECT as the driver parameters to this function, in which case Allegro will read hardware settings from the current configuration file. This allows the user to select different values with the setup utility: see the config section for details. Alternatively, see the platform specific documentation for a list of the available drivers. The cfg_path parameter is only present for compatibility with previous versions of Allegro, and has no effect on anything.

Return value: Returns zero if the sound is successfully installed, and -1 on failure. If it fails it will store a description of the problem in allegro_error.

See also: remove_sound, reserve_voices, detect_digi_driver, detect_midi_driver, set_volume, play_sample, Voice control, play_midi, play_audio_stream, install_sound_input, allegro_error, Standard config variables, set_mixer_quality, DIGI_*/DOS, DIGI_*/Windows, DIGI_*/Unix, DIGI_*/BeOS, DIGI_*/QNX, DIGI_*/MacOSX, MIDI_*/DOS, MIDI_*/Windows, MIDI_*/Unix, MIDI_*/BeOS, MIDI_*/QNX, MIDI_*/MacOSX.
Examples using this: exmidi, exsample, exsprite, exstream.
void remove_sound();

Cleans up after you are finished with the sound routines. You don't normally need to call this, because allegro_exit() will do it for you.
See also: install_sound, allegro_exit.
void set_volume(int digi_volume, int midi_volume);

Alters the global sound output volume. Specify volumes for both digital samples and MIDI playback, as integers from 0 to 255, or pass a negative value to leave one of the settings unchanged. Values bigger than 255 will be reduced to 255. This routine will not alter the volume of the hardware mixer if it exists (i.e. only your application will be affected).
See also: install_sound, set_hardware_volume.
void set_hardware_volume(int digi_volume, int midi_volume);

Alters the hardware sound output volume. Specify volumes for both digital samples and MIDI playback, as integers from 0 to 255, or pass a negative value to leave one of the settings unchanged. Values bigger than 255 will be reduced to 255. This routine will use the hardware mixer to control the volume if it exists (i.e. the volume of all the applications on your machine will be affected), otherwise do nothing.
See also: install_sound, set_volume.
void get_volume(int *digi_volume, int *midi_volume);

Retrieves the global sound output volume, both for digital samples and MIDI playback, as integers from 0 to 255. Parameters digi_volume and midi_volume must be valid pointers to int, or NULL if not interested in specific value.
See also: set_volume, get_hardware_volume.
void get_hardware_volume(int *digi_volume, int *midi_volume);

Retrieves the hardware sound output volume, both for digital samples and MIDI playback, as integers from 0 to 255, or -1 if the information is not available. Parameters digi_volume and midi_volume must be valid pointers to int, or NULL if not interested in specific value.
See also: set_hardware_volume, get_volume.
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