Hello everyone,
I am new to using REW and I need help to correctly interpret the frequential SPL graphics that I obtain when I measure the same sounds.
First of all, I am unsure about what reference is used to calculate the dB values shown on graphics obtained by using the "Measure" feature. The previous software I worked with was using the threshold of audibility (0.00002 Pa) as the dB reference and I am wondering if it is the same for REW.
Second of all, for now, I have taken a few measurements with REW, using the "Measure" feature where I have muted the sweep (by muting my speakers) and I have generated a tone of 500 Hz. I have run the measurements four times, and I obtain significant differences between the graphs. In fact, three of them are very similar, just as I expected them all to be, but there is one of them that is quite different. I understand that the SPL may be slightly different from a measurement to another, but what I would like to understand is why there would be such a sudden change in my measurements (see attachment).
Indeed, when I look at the first graph, the one of the ambient noise alone, I obtain a relatively linear and consistent spectrum. However, when I generate a tone, I obtain results where the low frequencies are under the 0 dB line, whereas the high frequencies are over it, and vice-versa. In short, I don't understand why those results do not even overlay with the ambient noise measurement I have made.
Can someone plus help me understand this? I would really appreciate the help.
I am new to using REW and I need help to correctly interpret the frequential SPL graphics that I obtain when I measure the same sounds.
First of all, I am unsure about what reference is used to calculate the dB values shown on graphics obtained by using the "Measure" feature. The previous software I worked with was using the threshold of audibility (0.00002 Pa) as the dB reference and I am wondering if it is the same for REW.
Second of all, for now, I have taken a few measurements with REW, using the "Measure" feature where I have muted the sweep (by muting my speakers) and I have generated a tone of 500 Hz. I have run the measurements four times, and I obtain significant differences between the graphs. In fact, three of them are very similar, just as I expected them all to be, but there is one of them that is quite different. I understand that the SPL may be slightly different from a measurement to another, but what I would like to understand is why there would be such a sudden change in my measurements (see attachment).
Indeed, when I look at the first graph, the one of the ambient noise alone, I obtain a relatively linear and consistent spectrum. However, when I generate a tone, I obtain results where the low frequencies are under the 0 dB line, whereas the high frequencies are over it, and vice-versa. In short, I don't understand why those results do not even overlay with the ambient noise measurement I have made.
Can someone plus help me understand this? I would really appreciate the help.