I am using a Window 7 machine with an 8 channel audio card to provide
multichannel outputs from a dedicated software application. The
application plays sampled pipe organ audio in response to Midi commands
from musical keyboards. Basically it's a virtual pipe organ. The
problem I'm having is that the processor (quad core AMD) speed changes
due to various things that can happen, such as overheating, etc. This
results is the audio board putting out a click or pop when the processor
speed is adjusted. I have change many parameters and have improved the
situation considerably, however, 1 pop or click is not acceptable. I
know many of the parameters must be adjusted in the BIOS, but I'm sure
there are some things that W7 does that affects this problem. Anyone
have any ideas?
Are you using the "Always On" power schema ? Visit the Power
control panel, and look for a schema that keeps the CPU at
full speed all the time.
Even if the processor was running at its lowest speed under Cool N' Quiet,
it would probably be enough to service the sound card. But what is
bad though, is P-state changes, which might take 100 microseconds or so.
I don't know if the CPU is available to execute instructions during
that transition. During a P-state change, VCore is adjusted and the
multiplier is changed, and the two changes are sequential. (And it
depends on whether the CPU is speeding up or slowing down, as to which
change is done first in the sequence.) When playing a video, I think
AMD systems have been known to make 30 P-state changes per second.
I don't know if that's the nature of where your click of pop is
coming from - a buffer underrun due to that 100 microsecond outage
sounds pretty unlikely to be enough to do it. The buffer is probably
a lot bigger than that, and the threshold should leave plenty of
time for it to get serviced when it needs to be filled up.
Other possibilities, are activities on the computer which are
not even visible as such, from the OS. Such as System Management
Mode or SMM. You can check for SMM activity, in an indirect
measurement way, using DPCLat. Certain Gigabyte boards show
spikes in DPCLat, implying long periods of time spent in SMM.
And, SMM could not be disabled. SMM is used for things, like
adjusting multi-phase VCore designs, while the system is running.
The change to the number of phases being employed, is done via
BIOS code running under SMM. The OS is blissfully unaware it
has been booted from the processor by SMM. (It's possible if you
were in SMM long enough, you could miss a clock tick interrupt.)
And DPCLat, uses the service time of Deferred Procedure Calls, to
indirectly determine something like SMM is happening.
I have no idea what OSes that program supports. It's a pretty
If you test out that program, and verify you don't have an SMM
problem, look in Task Manager, and see if you've acquired a
"LtcyCfgSvc.exe" process. It's possible that got installed
on my system when using DPCLat. I'm not really sure, but that's
about all I can associate it with on my main machine.
Typically, people who build audio workstations, test with DPCLat
to see if the motherboard is going to be a problem or not.
Gigabyte has released updates to the BIOS, that reduce spikes in
DPCLat, so it is possible to make improvements of the worst
cases (like, blowing a clock tick), caused by long SMM runtime.
(Some background on SMM, here.)
This would be an example of a motherboard with a serious problem.
The green bits are good. The red spikes, are not. The original
photo is no longer available, and all I can get is this crappy
Note that, there are some transitions on a PC, where there
are unavoidable long delays. I've noticed, entering or
exiting a 3D game, causes a large spike in DPCLat. So if you're
working in a recording studio, with an audio workstation,
don't run off and play Quake while you're recording a live act
Stick to playing Solitaire.