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Gravis Ultrasound Soundfont Software Mixing Routines

Gravis Ultrasound Soundfont Software Mixing Routines

In old games the software mixing routines are programmed for performance such that by default there wont be any interpolation.

On the Gravis Ultrasound (GUS) the base port address has to be jumpered.

A GUS uses a IRQ and DMA for playback and another IRQ and DMA for recording.

But this can be reduced as the same IRQ and DMA can be set for playback and record.

The restriction is that it is no longer possible to record and play sound at the same time.

Typically a GUS is used in a system paired with a Sound Blaster.

So a recommended setting is a jumpered base port of 240, IRQ 7 for playback and record and DMA 7 for record and playback.

Also some DOS4GW versions have a bug with hardware using DMA greater than 7).

For installation one can choose to run the whole GUS software setup 4.11 or just copy this ready setup folder.

It is a known bug that the GUS setup fails when checking for resources and reports problems specifically on DMA check.

It checks for a GUS at the port address given in the environment variable ultrasnd and reads further the desired IRQDMA values and sets the card accordingly.

After entering these two lines at the command prompt there is a quick test to see if the desired resources work by using a music player like XTC-PLAY with some music file.

If it freezes on loading the music file then the DMA setting it in conflict.

If the player plays a few seconds then stops and you can still exit by pressing ESC the playback IRQ is in conflict.

For the final autoexec.bat init part one more line has to be added.

A GUS has no direct output channel like Sound Blaster cards but uses a Digital Signal Processor (GF1) that can play from the cards own RAM.

The first GUS were released with 256 kB later models with 512 kB RAM.

This is strongly recommended as it poses a few advantages for playback quality.

To replay digital audio data it must be uploaded to the cards RAM first.

All audio data is resampled to the output playback rate using linear interpolation and mixed to stereo.

Since the computing power of the GF1 is limited the output sample rate drops gradually when using more than 14 active voices.

XM file and only 20 channels play a note at a certain moment the output sample rate will be 30870 Hz in this moment.

From performance considerations native GUS support for playback can help a 386 or 486 class system to save CPU load as a GUS mixes sound channel by its own.

Gravis Ultrasound Soundfont Full Load When

As example a 386DX-16 CPU is on full load when mixing 6 channels playback in 8 bit.

Also a fast Pentium CPU can be brought to its knee when playing a 32 channel song with high quality FPU interpolation in software.