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#### JohnM

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6,709 Posts
Hi Nick,

Glad you like the new features.

Broadly speaking, the difference between a spectrum plot and an RTA plot is in how the frequency content is treated. A spectrum plot shows the level of each frequency in its analysis range, dividing the range into "bins" of equal width in Hz. For example, a 65536 length spectrum at a 48kHz sampling rate has bins that are approx 0.7Hz wide. The spectrum treats the range between 20Hz and 20.7Hz the same way it treats the range between 20,000Hz and 20,000.7Hz. That can be useful when looking at distortion components, for example, but is very different from the way we hear. Our hearing, as a very rough approximation to a very complex subject, splits the frequency range into bins whose width is bigger at high frequencies than it is at low frequencies, in fact the width is a proportion of the frequency e.g. a bin of 1Hz at 100Hz would be treated with the same weight as a bin of 10Hz at 1000Hz or 100Hz at 10,000Hz. In each of those cases the proportion is 1%. An RTA works similarly, it has bins which are a constant fraction of an octave wide. An octave is a doubling of frequency, so how many Hz are in that fraction of an octave depends on the frequency - the octave from 100Hz to 200Hz spans a lot less range than the octave from 10,000Hz to 20,000Hz. The width of the horizontal bars in the RTA plot correspond to the width of the RTA bins. If you measure a pink noise signal with an RTA what you see corresponds with how your ear perceives things, a flat line on the RTA would mean you would perceive the levels as the same across the range.

A much shorter version of that is: you will almost always want to use the RTA views and almost always with some form of pink noise signal being played through your system

The levels of the RTA depend on the octave fraction used. The smaller the octave fraction, the narrower the bins that are being analysed. The RTA shows the energy in each bin, so as the bins get narrower the energy gets lower. With RTA plots we are more interested in the shape than the level, if everything is flat then we have even reproduction across the band.

As a final tip, you can make the RTA plots look nicer by "joining the dots" of the bins rather than having bars that are the width of each bin. You control that using the option in the View settings.

#### JohnM

Joined
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6,709 Posts
Set the mode to RTA rather than Spectrum, e.g. RTA 1/24 octave. What is the test signal you are feeding the system? Best would be to use "Pink PN" from the REW siggen.

#### JohnM

Joined
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6,709 Posts
Will the pink noise on the avia or DVE disks be a close approximation to the pink PN on REW?
No, they will be pink filtered random noise so if you use them you will need to use averaging on the RTA to see what is happening at low frequencies.

#### JohnM

Joined
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6,709 Posts
It’s mentioned that we don’t need calibration file if we do measurement through R channel
Not anywhere I've seen

does that mean I don’t need to perform the soundcard calibration steps to get a calibration file? Just loop back L channel while doing measurement is enough?
No

How to balance left and right channel when loop back one and use another for real measurement? What I understand in this case, R channel input is from Phantom powered Mic, and L channel input is directly from output whose signal is generated from REW. So what I shall do in order to balance them?
If each channels has its own input gain then adjust each gain as required. If the channels do not have separate gain (unusual if one is mic and one is line) you could alter the windows mixer balance control for the input.