Thanks you for the response Wayne. I may have set the levels to low when setting the Pref's. page. I kept getting a levels high warning when I went to the "Measures" and clicked on check levels. I adjusted the input vol. for the "input/mixer vol." box in order to get the levels down-where should I make adj. to the levels to make them acceptable for the REW program?Hey Bob,
The only thing wrong is that the level is WAY too low. The bulk if the reading should be running through the middle of the 75 dB Target.
Other than that it looks normal. All the raggedness is comb filtering, caused by reflections in the room. Only a ton of treatments would do away with it. Fortunately, our ears are very forgiving. Mics don’t “hear” the way our ears do.
Use 1/3 or 1/6-octave smoothing to get an idea of what the underlying trend in response is.
Regards,
Wayne
Hi Bill. So, I am correct to adjust the input vol. level? I will reset everything back to where it was and re-do my SPL.Hi Bob,
After you adjusted the "input/mixer vol." level, the actual levels from the speakers themselves were unchanged, right? If you modify the input volume level on the computer or on the preamp/mixer, you need to re-do the Calibrate SPL process to tell REW that the audible level is still 75dB even though the electrical level it sees has now changed.
Bill
Ok Bill. I reduced the input vol. level down to .199 (which reduced the levels to about 20-21), re-ran the SPL check, and set the SPL to 75db. Here is the pic of the graph I generated (BTW, I had both sp. on for the SPL check-is this ok?).Certainly, if you are observing clipping in the red lights on the preamp/mixer, or if REW is warning of excessive levels on the input channels, then you need to tweak the input volume downward at either the preamp or the computer. Whenever you change these, you need to redo the Calibrate SPL step, because you have changed the REW perceived electrical levels while the physical audio levels were unchanged. Because I never know if someone or some other application has changed the levels, I find it best to run the Calibrate SPL step at the start of each session.
Of course, if you are just interested in making the graph have the normal average level of 75dB, you can change the offset to the data to achieve the level you want to see, and can use the Add offset to data button to permanently modify that measurement.
Bill
Actually Bill, it was measured w/Audyssey OFF...! I do not understand why the rolloff.It doesn't matter per se whether you calibrate the SPL with one or both front speakers. Obviously, if you calibrate the levels to 75dB with both speakers and then you measure only one, the measured level will be lower than 75dB. If you calibrate the level to only one front speaker and then measure both together, the level will be higher than 75dB.
I assume you calibrated with both speakers on and then measured both together. Some of the variation you see in the graph comes from comb filtering between the two speakers, as Wayne mentioned above. You can eliminate this effect by measuring the left and right separately, but that can also uncover variation where one speaker shows dips that the other does not. You can also reduce its effect by using more smoothing.
I also assume the measurement was made with Audyssey on. In which case, much of the rolloff at the high end is a deliberate result from the Audyssey Reference curve.
Bill
