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In Reply to: Oversimplification. posted by carcass93 on February 3, 2011 at 10:53:40:
1. Perhaps there is a DAC out there that has excellent jitter immunity and still sounds good. There is no reason to believe that such a device is impossible, just not on the market yet.
2. I was citing one specific case that is unique to FLAC. Any activity has the possibility of changing things, but this one is sufficiently gross that it can even affect fan speed. :-)
3. Two possible reasons for the differences with your 10 minute task immediately come to mind:
First, the scheduling software in Windows may not be efficient, in which case every time the O/S checks what there is to do it has more work if there are additional possible candidates. (I don't know if that is the case with Windows, but it was definitely the case with other operating systems for their networking code.)
Second, when something is loaded into memory it will affect the location of other programs that are subsequently loaded into memory. The processing efficiency may be affected because two hot loops may be loaded in such a way that they are competing for the same cache line. The exact details will depend on the processor cache design and the order and size of memory allocations.
With proper instrumentation it would be possible to observe or eliminate both of these possibilities. Obviously, for best results you need separate test equipment to observe the operating system, as a measurement process in the system will itself affect what is being measured. Neverthe less it may be possible to ascertain what is going on by careful software implementation. One measurement of OS and CPU efficiency is system idle time for a given workload. However, you can't get this accurately using standard operating system measurement (e.g. Windows task manager). The reason is that the sample interval is probably correlated with operating system timer based functions. It may be possible to measure these effects by running a low priority CPU bound process in a "soak loop" and observing how system changes affect progress of this task. (Don't try this on a system that has minimal cooling.)
I'm sure there are more possibilities, these are just two of them. I think it is futile to attempt to optimize system software without having access, at minimum, to source code.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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Follow Ups
- Progress comes from appropriate simplification - Tony Lauck 11:53:21 02/03/11 (0)
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