Clicking Noises While Playing Sounds on Sound Blaster Feature
ID: Q76805
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The information in this article applies to:
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Microsoft Windows with Multimedia Extensions, version 1.0
SYMPTOMS
While playing some sounds on the Sound Blaster card, you may notice
periodic popping or clicking sounds. This generally occurs only when
running under enhanced mode Multimedia Windows.
STATUS
Microsoft is researching this problem and will post new information
here in the Microsoft Knowledge Base as it becomes available.
CAUSE
If a Sound Blaster board with versions 1.x of the Digital Signal
Processor (DSP) is installed and Multimedia Windows is running in
enhanced mode, a periodic click is audible when playing a wave file.
This is caused by interrupt latency, meaning that interrupts are not
serviced immediately. This causes the Sound Blaster to click because
the versions 1.x DSPs produce an interrupt when the current Direct
Memory Access (DMA) buffer is exhausted. The click is the time it
takes for the interrupt to be serviced by the Sound Blaster driver
(which is delayed by enhanced mode Windows).
MORE INFORMATION
The click is still present in standard mode, although it is much less
pronounced because the interrupt latency is less. The click is more
pronounced for pure tones.
The version 2.0 DSP solves this problem by using the auto-initialize
mode of the DMA controller (the 8237). In this mode, the DMA
controller automatically reloads the start address and count registers
with the original values. In this way, the Sound Blaster driver can
allocate a 4K DMA buffer; using the lower 2K as the "ping" buffer and
the upper 2K as the "pong" buffer.
While the DMA controller is working on the ping buffer, the pong
buffer can be updated; and vice versa. Therefore, when the DMA
controller auto-initializes, it will already have valid data
available. This removes the click from the output sound.
However, Windows 3.0 enhanced mode does not support the
auto-initialize mode of the DMA controller. Therefore, Multimedia
Windows provides a virtual device driver (VxD) called VADMAD.386
(virtual auto-initialize DMA device) that attaches itself to the
virtual DMA device (VDMAD). Its purpose, as the name implies, is to
support the auto-initialize mode of the DMA controller. However,
VADMAD.386 does not FULLY support this mode -- it was designed only to
correct the problem with the Sound Blaster.
Sound Blaster is manufactured by Creative Labs, a vendor independent
of Microsoft; we make no warranty, implied or otherwise, regarding
this product's performance or reliability.
KBCategory: kbmm kbsound
KBSubcategory: win31
Additional query words:
1.00 auto initialize autoinitialize MMWIN
Keywords :
Version : :1.0
Platform :
Issue type :