Articles

AGI Sound Tutorial v1.0

by Nick Sonneveld
Last Updated 4th March, 2002

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2. Limits of the AGI Sound Format

The AGI sound format is modeled around the PCjr's sound chip.  Because of this, we have to work around the idiosyncracies of that particular chip.  This involves:

• having three voice channels
• one noise channel
• can only define frequencies between the range of 110Hz to 111860Hz
• noise channel only has 3 different frequencies, or you can "borrow" the frequency from the third channel.
  
• creating AGI sounds from other formats create large files.  The AGI interpreter has a very limited memory space.
• PC interpreter only plays the first channel and ignores the rest.
• sound resources cannot be discarded without calling a new room in the PC interpreter.  You have to make sure all sounds are loaded at the start of each room.
  

Most of these we could work around by defining a new backwards-compatible format for the new interpreters but we still want to support the original Sierra interpreter.  With simple music and a bit of originality, it shouldn't be too hard to create music for your game.  Sierra's Police Quest had pretty realistic gun noises (if you had a computer that could play them).

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