Sound level for measurements

[Truett]

I have not been able to follow any of the instructions I have seen calibrating with the DB meter. At one point it said calibration not necessary using HDMI output. So I am not confident in my test levels. When I click check levels, I don't hear anything.

Right now I have done the measurements using -12 DB on my Trinnov processor. But I have also done measurements using - 16 and -20, and each time it shows the frequency response graph just a bit lower.

I assume that measurements should all be done the same for comparison purposes. Right? What should I be doing to ensure the correct measurement levels and consistency if necessary?

 

[John Mulcahy]

There are two kinds of calibration. A soundcard calibration measures the overall frequency response shape from output back to input, that isn't generally relevant if you are using an HDMI output or if you use a USB mic for input. Calibrating the SPL reading ensures REW shows correct SPL figures, but that isn't applicable if you use a USB mic for measurement.

To make it easy to compare your measurements it is best to stick with the same sweep level and replay volume level, ones that give levels during measurement that are comfortable.

 

[Truett]

There are two kinds of calibration. A soundcard calibration measures the overall frequency response shape from output back to input, that isn't generally relevant if you are using an HDMI output or if you use a USB mic for input. Calibrating the SPL reading ensures REW shows correct SPL figures, but that isn't applicable if you use a USB mic for measurement.

To make it easy to compare your measurements it is best to stick with the same sweep level and replay volume level, ones that give levels during measurement that are comfortable.

So when using a USB mic and an HDMI output, do I never make volume adjustments in REW? Only on the AV processor volume?

And how do I know that -12 DB on the processor volume is okay? Or that -18 or -20 is okay? I assume that I should pick a volume level and stick with it forever. How do I know it is a good volume level? And why does my REW check levels button not do anything?

 

[John Mulcahy]

I should pick a volume level and stick with it

Yes.

How do I know it is a good volume level?

Around 75 dB is fine, similar to the level calibration signal of an AV receiver.

why does my REW check levels button not do anything?

It sends a signal, but your system may not be reproducing it. The signal that is sent depends on the measurement settings. If you are measuring to a low end frequency REW will send a sub cal signal, if you are measuring to a high end frequency it will send a speaker cal signal. If you are using a high end frequency to measure a sub the sub will likely not reproduce anything audible from a speaker cal signal (and much of the measurement result will be noise).