questions about phase measurement with REW +umik1

[vinjoutw]

New to REW,
Can REW guru help on below questions concerning phase measurement using REW+Umik1?
1. What kind of phase information I get when I measure with REW+Umik1
2. Can I adjust the phase condition with REW+Umik1 measured results
3. Compare to another commercial software Smaart, what are the differences between REW+Umik1 and Smarrt in phase measurement results?

Thank you very much

 

[Harrycr]

I'm no guru.
With any meaningful phase timing you need to have a reference with a tweeter. So with REW + UMIK (or any USB mic) it is essential to turn on Acoustic Timing in the preferences.
To phase align (alignment tool) a sub with speakers this is were phase can be useful.
In regards to Smaart I have never used it and you probably will find majority of people will be the same. REW would be the most used and liked by majority of people, including acousticans.
If you read the help files there is info on this. What I suggest is search "phase" in the help files this will bring up all you need.

Hope this helps a little.

 

[John Mulcahy]

Phase data depends on the position of time zero on the Impulse response. For a single measurement a suitable position can be estimated, for example using REW's Estimate IR Delay function. To compare phase in separate measurements they need to share some common timing reference. That would often be provided by a loopback connection to another soundcard input, as it is for SMAART, but USB mics generally do not have an additional input so a different method is required. REW offers an acoustic timing reference option, which sends a high frequency sweep to one reference speaker. Times are then relative to the detected sweep from the reference and will be consistent across multiple measurements as long as the reference speaker and the mic are not moved.

Having a reference is half the battle of getting meaningful phase information. The other half is removing fixed time delays, such as the time it takes for sound to travel from the speaker to the mic or processing times in equipment in the audio path. In SMAART the delay finder estimates and removes those delays, applying the time offset to subsequent measurements. In REW Estimate IR Delay can be used to set the value of the timing offset for subsequent measurements.

 

[vinjoutw]

thank you for your explanation. I wonder if it will be more accurate to use a Mic interface box for loopback connection than acoustic timing reference? I am using REW for digital crossover arrangement, so the phase alignment for high frequency/mid range/bass should be more accurate

 

[vinjoutw]

One more question is for Smaart, the test signal is continuous pink noise, but REW is using frequency sweep, will the phase measurement means the same thing?

 

[John Mulcahy]

The stimulus type does not affect the phase result. A loopback connection could be more consistent than an acoustic reference if the environment has a lot of reflections.