PRB: Clicking Noises While Playing Sounds on SoundBlaster Card

• Microsoft Windows Software Development Kit (SDK), versions 3.0 and 3.1

SYMPTOMS

While playing some sounds on earlier models of the SoundBlaster card, some periodic popping or clicking sounds may occur. These cards are generally referred to as the 1.0 DSP (digital sound processing) design. Cards using the version 2.0 DSP design can use version 1.5 of the SoundBlaster Multimedia Device Driver (SNDBLST2.DRV), which eliminates this situation.

CAUSE

This problem generally occurs only when running under enhanced mode Windows. It is a result of the current design of the SoundBlaster hardware, in conjunction with the interrupt latency inherent in enhanced mode Windows.

The SoundBlaster uses DMA (direct memory access) to transfer small pieces of the sound data from main memory to the card, and generates a hardware interrupt only when its buffer becomes empty. Upon receipt of this interrupt, the SoundBlaster driver prepares the next piece of sound data and initiates another DMA transfer. This process continues until the sound has been completely played out.

When running in Windows enhanced mode, the interrupt latency is often more than a few sample periods, which results in the noises discussed earlier.

RESOLUTION

Creative Labs has corrected the problem with version 2.0 DSP along with version 1.5 of the Sound Blaster Multimedia Device Driver. In addition, the new card from Creative Labs, the Sound Blaster Pro, does not exhibit the clicking problem. Contact Creative Labs to update earlier Sound Blaster cards to version 2.0 DSP.

For testing purposes, this problem can be resolved by running in Windows standard mode, where interrupt latencies are lower.