AHI

APIs and OS Components

AHI is the de facto retargetable audio standard for Amigoid computers, developed by Martin Blom. It first became popular in the mid- to late-1990s. Programs supporting the AHI standard ensure that a user will be able to use the software with any sound card for which there is an AHI driver available. Virtually all Amiga-specific sound cards support AHI.

In an early anticipation of hardware independency, an AHI driver was also written for the Amiga's Paula chip, with the exepctation that future software would use calls to ahi.device rather than the native chipset's audio.device (However, the implementations of audio.device on MorphOS and AmigaOS4 automatically redirect to AHI, thus making many older, pre-AHI programs functional on the newer systems).

Though Paula can normally only produce 4 channels of 8-bit sound, the Paula AHI driver can make use of a technique called subranging, where one channel plays the upper 8 bits at a volume of 64 and the other channel plays the lower 8 bits at a volume of 1. This allows the chip to "fake" several 14-bit sound modes.

An installed AHI system provides an Audio Database of available audiomodes (analagous to the Screenmode Database for display options), allowing the user to select the best mode and mixing frequency based on a variety of requirements, such as RAM availability, CPU power, sound card capability, and application demands. Some programs allow the direct selection of an audiomode, others allow the user to select a preconfigured unit, and still others will default to the Music Unit, as set in the AHI preferences tool.

AHI is available for AmigaOS, AmigaOS4, MorphOS, Amithlon and AROS.