Do I need to calibrate TrueRTA with the voltmeter if all I am using it for is the audio analyzer?
No. You only need to calibrate it if you are going to make voltage measurements where the absolute voltage or dBu level must be known. If you are only interested in relative measurements like “there is a peak of +6.25 dB at 500 Hz compared to the rest of the response” then voltage calibration is irrelevant. If you do not calibrate TrueRTA then the actual Line-In and Line-Out levels will be unknown. When you set the generator output level to -10 dBu the actual output level may be considerably higher or lower. Similarly, an input signal that reads -10 dBu may actually be higher or lower in level.
