Reply by John Herman July 21, 20072007-07-21
In article <W6qmi.39506$Um6.14540@newssvr12.news.prodigy.net>, "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote:
> >"Steamer" <personalemailcl@yahoo.com> wrote in message >news:Ji9mi.766$Dx2.714@newssvr17.news.prodigy.net... > >> The two audio signals, identical but with one delayed in time, are not >> available for measurement at the same physical location, which is what >makes >> the problem interesting. They are at different locations. We want to >> measure audio path propagation time through two sets of equipment on two >> different routes at two different destinations. A common highly-accurate >> time reference is available in both locations. >> >> Our goal is to detect a unique event in the audio path and to record its >> time of occurrence relative to our common time reference, at each >> destination. The difference in detection times represents the relative >> delay in the two audio paths. >> >> So I think the key question is: how accurately can a pre-defined audio >event >> (a data pattern after digitizing the audio) be time-tagged? We are not >> limited by noise, ADC resolution or sampling rate. > >If there is no noise and no distortion, then you can measure the time of >arrival with the infinite accuracy. So, it comes to the question of how good >is the actual channel. It also depends on the pattern that you are >triggering on. Taking the reasonable assumptions, it looks fairly simple to >achieve the accuracy of tens of microseconds, however it would not be very >easy to get to 1uS. > >Vladimir Vassilevsky >DSP and Mixed Signal Consultant >www.abvolt.com >
And how accurately do you know the time? I had a lecture on time long, long ago and it's not that easy to get time as seperate locations to 250 nanoseconds of accuracy. And as implied above, what is the signal to noise ratio? It would have to be very high, maybe 60 dB, maybe more.
Reply by Vladimir Vassilevsky July 15, 20072007-07-15
"Steamer" <personalemailcl@yahoo.com> wrote in message
news:Ji9mi.766$Dx2.714@newssvr17.news.prodigy.net...

> The two audio signals, identical but with one delayed in time, are not > available for measurement at the same physical location, which is what
makes
> the problem interesting. They are at different locations. We want to > measure audio path propagation time through two sets of equipment on two > different routes at two different destinations. A common highly-accurate > time reference is available in both locations. > > Our goal is to detect a unique event in the audio path and to record its > time of occurrence relative to our common time reference, at each > destination. The difference in detection times represents the relative > delay in the two audio paths. > > So I think the key question is: how accurately can a pre-defined audio
event
> (a data pattern after digitizing the audio) be time-tagged? We are not > limited by noise, ADC resolution or sampling rate.
If there is no noise and no distortion, then you can measure the time of arrival with the infinite accuracy. So, it comes to the question of how good is the actual channel. It also depends on the pattern that you are triggering on. Taking the reasonable assumptions, it looks fairly simple to achieve the accuracy of tens of microseconds, however it would not be very easy to get to 1uS. Vladimir Vassilevsky DSP and Mixed Signal Consultant www.abvolt.com
Reply by Steamer July 14, 20072007-07-14
Thanks to those above who have offered comments, but I see my explanation 
may have been misleading.

The two audio signals, identical but with one delayed in time, are not 
available for measurement at the same physical location, which is what makes 
the problem interesting.  They are at different locations.  We want to 
measure audio path propagation time through two sets of equipment on two 
different routes at two different destinations.  A common highly-accurate 
time reference is available in both locations.

Our goal is to detect a unique event in the audio path and to record its 
time of occurrence relative to our common time reference, at each 
destination.  The difference in detection times represents the relative 
delay in the two audio paths.

So I think the key question is: how accurately can a pre-defined audio event 
(a data pattern after digitizing the audio) be time-tagged?   We are not 
limited by noise, ADC resolution or sampling rate.

Thank you.




"George" <gmwemail-dsp@yahoo.com> wrote in message 
news:fLYli.46286$5j1.36759@newssvr21.news.prodigy.net...

> What I'm trying to do is to measure the amount of time shift between two > audio channels that are identical but shifted in time from one another > (because the delayed signal has passed through equipment whose propagation > time we wish to determine). > > There is a detector on each of the two audio paths. In each detector, > analog audio feeds the ADC, then a processor looks at the digitized audio > for a pre-specified signal event that will be used as a time marker. When > that event occurs, the processor recognizes it and generates a strobe > output. The time difference in strobe outputs of the two procesors > represents the time shift between the two audio paths. > > The amount of time needed to detect the signal event and generate the > strobe doesn't matter, as long as it's the same - to better than a > microseond - in both detectors. We expect something around a microsecond > of audio delay, so we need a measurement accuracy better than that. > > Appreciate your help with this problem. > >
Reply by Vladimir Vassilevsky July 14, 20072007-07-14
"Jerry Avins" <jya@ieee.org> wrote in message
news:SIKdndH9VdcjXwXbnZ2dnUVZ_hOdnZ2d@rcn.net...

> > What I'm trying to do is to measure the amount of time shift between two > > audio channels that are identical but shifted in time from one another > > (because the delayed signal has passed through equipment whose
propagation
> > time we wish to determine). > > > > Assuming baseband, the technique you want is cross correlation. No > special event markers are needed. In fact, broadband noise is an > excellent test signal for you.
Cross correlation of the noise like signals would be very demanding in the computation and not optimal for the SNR. I would measure the phase shift at the sinewave of the highest frequency. Resolving the ambiguity of +/- number of periods is not a problem either. Vladimir Vassilevsky www.abvolt.com
Reply by Jerry Avins July 14, 20072007-07-14
George wrote:
> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message > news:itXli.11302$bz7.3194@newssvr22.news.prodigy.net... > >> snip< > >> What exactly are you trying to do? >> > > What I'm trying to do is to measure the amount of time shift between two > audio channels that are identical but shifted in time from one another > (because the delayed signal has passed through equipment whose propagation > time we wish to determine). > > There is a detector on each of the two audio paths. In each detector, > analog audio feeds the ADC, then a processor looks at the digitized audio > for a pre-specified signal event that will be used as a time marker. When > that event occurs, the processor recognizes it and generates a strobe > output. The time difference in strobe outputs of the two procesors > represents the time shift between the two audio paths. > > The amount of time needed to detect the signal event and generate the strobe > doesn't matter, as long as it's the same - to better than a microseond - in > both detectors. We expect something around a microsecond of audio delay, so > we need a measurement accuracy better than that. > > Appreciate your help with this problem.
First, how does FM come in? If your audio baseband, of modulated in some way? If modulated, what it the carrier? Assuming baseband, the technique you want is cross correlation. No special event markers are needed. In fact, broadband noise is an excellent test signal for you. Jerry -- Engineering is the art of making what you want from things you can get. &macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;
Reply by Hendrik van der Heijden July 14, 20072007-07-14
George schrieb:

> What I'm trying to do is to measure the amount of time shift between two > audio channels that are identical but shifted in time from one another > (because the delayed signal has passed through equipment whose propagation > time we wish to determine). > > There is a detector on each of the two audio paths. In each detector, > analog audio feeds the ADC, then a processor looks at the digitized audio > for a pre-specified signal event that will be used as a time marker. When > that event occurs, the processor recognizes it and generates a strobe > output. The time difference in strobe outputs of the two procesors > represents the time shift between the two audio paths.
It should be easier and more accurate to sample both signals for some time using the same clock and calculate a cross correlation between them to get the delay. You may sample both signals using a stereo ADC (sound card?) to have a common time base. Hendrik vdH
Reply by Steamer July 14, 20072007-07-14
Posted from another office computer, sorry.

"George" <gmwemail-dsp@yahoo.com> wrote in message 
news:fLYli.46286$5j1.36759@newssvr21.news.prodigy.net...
> > "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message > news:itXli.11302$bz7.3194@newssvr22.news.prodigy.net... > >>snip< > >> What exactly are you trying to do? >> > > What I'm trying to do is to measure the amount of time shift between two > audio channels that are identical but shifted in time from one another > (because the delayed signal has passed through equipment whose propagation > time we wish to determine). > > There is a detector on each of the two audio paths. In each detector, > analog audio feeds the ADC, then a processor looks at the digitized audio > for a pre-specified signal event that will be used as a time marker. When > that event occurs, the processor recognizes it and generates a strobe > output. The time difference in strobe outputs of the two procesors > represents the time shift between the two audio paths. > > The amount of time needed to detect the signal event and generate the > strobe doesn't matter, as long as it's the same - to better than a > microseond - in both detectors. We expect something around a microsecond > of audio delay, so we need a measurement accuracy better than that. > > Appreciate your help with this problem. > >
Reply by George July 14, 20072007-07-14
"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message 
news:itXli.11302$bz7.3194@newssvr22.news.prodigy.net...

>snip<
> What exactly are you trying to do? >
What I'm trying to do is to measure the amount of time shift between two audio channels that are identical but shifted in time from one another (because the delayed signal has passed through equipment whose propagation time we wish to determine). There is a detector on each of the two audio paths. In each detector, analog audio feeds the ADC, then a processor looks at the digitized audio for a pre-specified signal event that will be used as a time marker. When that event occurs, the processor recognizes it and generates a strobe output. The time difference in strobe outputs of the two procesors represents the time shift between the two audio paths. The amount of time needed to detect the signal event and generate the strobe doesn't matter, as long as it's the same - to better than a microseond - in both detectors. We expect something around a microsecond of audio delay, so we need a measurement accuracy better than that. Appreciate your help with this problem.
Reply by Vladimir Vassilevsky July 14, 20072007-07-14
"Steamer" <personalemailcl@yahoo.com> wrote in message
news:UOTli.21839$RX.12605@newssvr11.news.prodigy.net...
> Hi all, > > I need to sample a 100 Hz - 15 kHz analog FM audio (music and speech) > channel for an unusual purpose - to measure the time that certain audio > events occur. > > Audio quality, resolution, distortion are only important to the extent
they
> affect the time accuracy of event detections. > > I'd like to be able to detect the occurrence of specific audio events in
the
> channel with an accuracy of better than one microsecond. This will be a
new
> design so there are no restrictions on sampling rate, choice of ADC etc.
Measuring arrival time with the accuracy of 1/100 of the bandwidth is not going to be very simple. You may need specially crafted signals and a precisely calibrated channel.
> Can anyone point me in the right direction please?
What exactly are you trying to do? Vladimir Vassilevsky www.abvolt.com
Reply by Steamer July 13, 20072007-07-13
Hi all,

I need to sample a 100 Hz - 15 kHz analog FM audio (music and speech) 
channel for an unusual purpose - to measure the time that certain audio 
events occur.

Audio quality, resolution, distortion are only important to the extent they 
affect the time accuracy of event detections.

I'd like to be able to detect the occurrence of specific audio events in the 
channel with an accuracy of better than one microsecond.  This will be a new 
design so there are no restrictions on sampling rate, choice of ADC etc.

Can anyone point me in the right direction please?

Thanks in advance.