[music-dsp] Recording very long sound files
tothl at inf.u-szeged.hu
Wed Sep 14 07:41:28 EDT 2011
On Wed, 14 Sep 2011, Richard Dobson wrote:
> How is the recording controlled - some external timer telling the process
> to start and stop?
Actually, we are recording a fixed number of samples (which is calculated
from the sampling rate). So we ask the system time - record N samples -
ask the system time. The difference between the two time instances should
be 8 hours, but in most cases it is somewhat longer. The difference varies
> Are you sure it is not simply a slight difference in start/stop times?
In most cases it's slight, but in eight days of testing it was 1 minutes
in one case on 5 minutes in another case - so unfortunately the whole
system seems unreliable.
> Do you actually find discontinuities in the recording?
We want to avoid listening to dozens of hours of recordings. Also, the
recordings are made for a sleeping center, so they contain the sound
people give during sleeping - in most cases just some very low-frequency
> You are using long long to index this aren't you?
I hope my programmers are better than committing such basic mistakes.
Also, in that case the difference would be fixed, while in our case it
varies from day to day.
> Personally I'd set up a machine with ntp time sync and for each packet
> you read from the sound card make a log of the number of samples you've
> seen so far and the PC time (sycned to network time).
I'm afraid we cannot synchronize to network time, as the whole equipment
is set up in a hospital room. But otherwise the idea is good, we'll try to
do some more detailed logging of packages and times.
Thanks to everybody who replied.
Hungarian Academy of Sciences *
Research Group on Artificial Intelligence * "Failure only begins
e-mail: tothl at inf.u-szeged.hu * when you stop trying"
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