Impulse "chirp x 2 ?

[Lesmor]

This has been bothering me for a while
when using acoustic timing I seem to be getting 2 "chirps"
one from the target speaker as expected at the start of the sweep, but I then hear a second "chirp" near the end of the sweep from my right side surround spealer
I am sure it never used to be like that
when visiting a friend I noticed the same thing happening on his system
is this normal?

 

[John Mulcahy]

There are two timing signals, both from the reference speaker, when the Analysis preference "Adjust clock with acoustic ref" is selected. REW uses the time between the signals to work out the difference between the replay and record clock rates. If a timing signal is coming from the wrong speaker that suggests a problem with the HDMI connection. Long cables can cause that.

 

[Lesmor]

Hi John thanks for the quick reply
I will check the preferences page
as per my OP I couldnt say I ever noticed 2 chirps before but the second is definately not coming from the reference speaker
I am using a 3 meter HDMI so that might account for it
all the best
Andy

 

[sm52]

REW uses the time between the signals to work out the difference between the replay and record clock rates

Can REW display somewhere what sample rate is detected on the device being measured? For example, when you click on the info button, among other information, add a line that the sampling rate on the measured device is such and such.

 

[John Mulcahy]

If there was any clock adjustment it is shown in the Info panel for the measurement and in the measurement notes.

 

[sm52]

For example, "Clock adjustment: -80,2 ppm" ? The difference in sampling rates is interesting. In Hz.

 

[Lesmor]

Just for completion I checked preferences analysis and Adjust clock with acoustic ref is ticked
is thia a requirement?
or can it be unticked

 

[John Mulcahy]

It is not a requirement. A USB mic like UMIK-1 gets its clock from the PC's USB interface, which is likely to differ from the clock in the replay device. That doesn't have much effect on the frequency response magnitude, but it will affect the phase response and the appearance of the impulse response. The clock adjustment corrects for that.

 

[John Mulcahy]

For example, "Clock adjustment: -80,2 ppm" ? The difference in sampling rates is interesting. In Hz.

ppm is the normal unit for clock accuracy and variation. If you want the absolute frequency it can be worked out approximately by multiplying that figure by the nominal clock rate. If the rate was nominally 48 kHz that would be (-80.2*10-6)*48000 = -3.8496 Hz, but that figure cannot be exact as neither clock rate is known, all that can be determined is how the clocks relate to each other.

 

[sm52]

The difference of 3 Hz from 48,000 Hz is very small. I was wondering if the playback time of the same music track on different devices will be different? I already understood that the difference will be in fractions of a second for a 3-minute track. The second question is, will there be differences when decoding audio data on devices with slightly different sample rates? How do you think?