REW add delay in measurement file

[Robin Rose]

Hi everyone, I have been using new to do some measurements on an and project for school work.

I have been able to get right and left speaker frequency response curve.

What I want to do now is to send a sweeping sinusoid on the left speaker and the same signal on the right with a 2ms delay (for ANC).

I tried creating a stereo file with python with delay on the right channel but I can't use it for measurement in REW.

Is there a way to solve this ?

Thank you, have a good day ?

 

[John Mulcahy]

I tried creating a stereo file with python with delay on the right channel but I can't use it for measurement in REW.

Do you mean you took an REW-generated sweep file and created a new file from it with the R channel delayed? You should be able to use that, just tell REW you are using the original file it produced.

 

[Robin Rose]

Yes a rew generated sweep, I converted it into a numpy array, add some zeros at the end for the left channel and some at the begining for the right channel (to have the same lenght) for the delay and exported it as wav but REW doesn’t accept it.

Is it possible to add the delay only in rew ?

 

[John Mulcahy]

You can't delay sweeps in REW. Just load the original file in REW, it is only interested in the first couple of dozen samples in each channel as info is included in them to tell REW what kind of sweep is present. REW doesn't use the contents of the sweep file since that would be subject to quantisation depending on the file format.

 

[Robin Rose]

So I use my python program to add zeros after the first 100 samples (so that REW can then read it) for the delay and it should work ?

 

[John Mulcahy]

REW only reads the initial samples which contain the information it needs, it ignores everything else in the file and just shows an image of the contents. Nothing you change in the file will have any effect on what REW does with the measurement. That's why I keep telling you to load the initial, unmodified file in REW. You can play back your modified file when you make the measurement.

 

[Robin Rose]

So if I understand, I can't modify any measurement file created by REW to add delay because REW won't read it the way I want.

Is there a way to have REW make a measurement with a sweep on the left channel and the same input on the right channel with a 2ms delay for the ANC ?

I thought REW was used to test surround system, so I thought you could use time delay on one of your speakers if they were not at the same distance from the mic.

Do you know a third-party app on Mac that would allow me to do this ?

 

[John Mulcahy]

No, I don't think you understand it yet. When you measure from file REW needs to know what kind of sweep settings were used for the file. It gets that information from the sweep file.

There are several ways you can produce the effects of delay in a channel:

1. In the graph controls there is an "Offset t=0" control that allows the timing of a measurement to be shifted relative to the t=0 reference time. That will only make sense for a measurement of a single channel.
2. The speaker to be delayed could be moved further away by the corresponding distance
3. You could use your modified sweep file, with the data for the channel which does not have the timing reference delayed by the desired amount, which means it will play back later (relative to the timing reference)

All have the same effect on the measurement result for a single channel. If you want to measure the effects of two channels playing with a delay added to one of them options 2 and 3 can still be used, or option 1 could be used to delay a measurement of the channel that is to be shifted and the result could be added to a measurement of the other channel using trace arithmetic.

Does that help? Per the previous posts, you can use your modified file to play the sweep(s) but load the original, unmodified file in REW.