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AmigaOS 4.0 - About OS4 - Preferences

AHI Preferences Editor
The AHI Preferences editor is used to set the Audio Card Configuration, and currently supports only FM801, SB 128 (Esoniq), and SB Live/Audigy 1 & 2 (EMU10kx) based cards.

Mode Settings
The first panel is used to configure the Mode settings, in this example showing the default settings for the 'Music unit'. While most programs use the Music unit, some programs use one of the other units (Unit 0, Unit 1, Unit 2 or Unit 3), so those need to be configured as well. In this example we are using the SoundBlaster Live! which utilises the EMU10kx chipset, although we also have the AC97 chipset built into the motherboard, so the available driver modes must match the audio chipsets you have installed.

Audio mode for EMU10kx can be
16 bit mono
16 bit stereo
HiFi 16 bit 7.1 multichannel
HiFi 16 bit mono
HiFi 16 bit stereo

Frequency range 8000Hz to 48000Hz

Channels range 1 to 32 except for Music Unit where forced to 32

Volume range Muted to +12.0dB

Monitor range Muted to +12.0dB

Gain range +0.0dB to +22dB

Input can be set to Mixer, Line in, Mic, CD, Aux, Phone, Video, and Mixer (mono), by moving the slider

Output can bet set to Front, or Front & Rear, by moving the slider

There is also a 'Play a test sound' button to test that everything is working.

The following modes are available for most drivers:
Mono Mono output, all sounds will be centered, and no surround sound is possible.
Stereo Stereo output, but all sounds are either forced to the extreme left or extreme right, i.e centered sounds are not possible. This mode will probably use slightly more CPU power than the "mono" mode. Since all sounds are forced to one of the extreme positions, stereo sounds will play with either the left or the right part muted.
Stereo++ Stereo output with free positioning of all sounds, for example, an instrument can be placed anywhere between the two speakers. Unless the program only uses the extremes when positioning a sound, this mode will use more CPU cycles than the "stereo" mode.
Fast mono
Fast stereo
Fast stereo++
"Fast" modes take some shortcuts in order to reduce the CPU usage. For 8 bit samples, multiplication tables will be used, which speeds up mixing by magnitudes and still gives the same quality with the exception of volume levels; instead of 256 levels only 32 are available. The disadvantage of multiplication tables is that they require a fair amount of free RAM. For 16 bit samples, the shortcuts are a bit more crude; the volume of each sound will be rounded to a power of 2 before it's played. This means that a 16 bit sound will only be played at volume levels of 100%, 50%, 25%, 12.5% etc. If surround sounds are played, the normal (not "fast") mixing routines will be used. You can use the Advanced Settings Page to disable surround sounds for "fast" modes. "Fast" modes are useful if you wish to use as little CPU power as possible, but don't mind spending some memory to reach that goal. They are also very useful when playing 16 bit audio streams, for example from a sample or MPEG player, since that usually doesn't involve volume scaling and frequency recalculation. However, if used for playing streams, make sure the mixing frequency is the same as the stream frequency!
HiFi mono
HiFi stereo
HiFi stereo++
"HiFi" modes use much better mixing algorithms than the other modes, using 32 bits internally and linear interpolation. They are also much slower than the other modes. "HiFi" modes turn on master volume with clipping automatically. "HiFi" modes are useful when you're playing music, for example MIDI songs or modules, and want the best possible quality AHI has to offer.

Advanced Settings
When you click on the Advanced settings tab another panel shows more configuration parameters which are applicable to all units.

Under Global options:

Debug level can be set to 'None', 'Low', 'High' or 'Full' and when set output is via the serial port.

Echo will be set to 'Enabled' but is ghosted out and cannot be changed.

Surround in "Fast" modes will be set to 'Enabled' but is ghosted out and cannot be changed.

Master volume will be set to 'With clipping' but is ghosted out and cannot be changed.

CPU usage limit range is 0% to 100% (if set too high, excessive CPU activity may slow other programs)

Default anti-click time has a range of 0ms to 100ms, and can be used to reduce the ramping when playing sound samples. Default is 1ms.

Volume scaling can be set to 'Safe', 'Safe, Dynamic', 'Full volume', '-3dB' or '-6dB'. Default is 'Full volume'.

Action Buttons
When you make changes you can choose to 'Save' them permanently, just 'Use' them temporarily until the system is rebooted, or you can 'Cancel' and lose all changes.

More on AHI
While applying updates to software is beyond the scope of these pages, the AHI modules have been updated several times causing strife for many users, so we will make the exception here.

AHI updates are accessible from OS4 depot and are supplied in an lha file which must be unarced before it can be used and it contains two main components. The 'AHI' file in the Prefs drawer must be copied to the Prefs drawer on your SYS: disk, and the 'ahi.device' file in the devs drawer must be copied to the Devs: drawer on your SYS: disk. The install notes may refer to requiring a particular version of the audio card driver, and because it is hardware dependent, it is not supplied. To check the version details of the audio card driver, use the sizing gadget to drag the Mode settings panel to fill the screen as shown below:

In the panel at bottom left it shows the Driver details and the Version currently installed. If it is not the correct version then download the appropriate driver from OS4 depot, unarc the lha file and copy the contents to the appropriate folders.

The drivers come in two parts. The audio files (e.g. emu10kx.audio, via-ac97.audio, etc) must be saved in Devs:AHI while the mode files (e.g EMU10KX, VIA-AC97, etc) must be stored in Devs:AudioModes. Multiple drivers can be stored and where AC97 is fitted, you can switch between AC97 and the alternate sound card if required.

Return to Preferences Selection

Disclaimer: Amiga Auckland have prepared the above information for the use of its members based on our experiences and as such is subject to revision at any time. Amiga Auckland cannot guarantee any of the information and cannot be held accountable for any issues that may result from using it.

Copyright 2006 Amiga Auckland Inc. All rights reserved.
Revised: February 9, 2006.