Bo Deadly
Well-known member
I want to measure SNR of a simple API style mic-pre. I have a QA400 audio analyzer but I need to attenuate the stimulus to keep the output within the maximum limits of the QA400 (only ~3.9 Vpp). So the QA400 is not going to give me an accurate SNR value if I'm messing with the gain by attenuating and then amplifying by 40+ dB.
So is there a way to guesstimate what the SNR would be if I did not need to attenuate / amplify?
Here is a block diagram of the rig:
Using the oscilloscope I measured the Vpp at 3 points:
Output of QA400: 2.85 Vpp 2.3 dBu
Input of mic-pre: ~16.5 mVpp -42.4 dBu
Output of mic-pre: 3.9 Vpp 5.0 dBu
So overall gain looks like it's about +47.4 dB.
The QA400 reports the SNR as 87.4 dB but I think it should be much better than that because I'm attenuating the input stimulus. So is there a way to compute what the SNR is theoretically?
Not that it should matter but here is a pic of the mic-pre and how the QA400 is hooked up:
So is there a way to guesstimate what the SNR would be if I did not need to attenuate / amplify?
Here is a block diagram of the rig:
Using the oscilloscope I measured the Vpp at 3 points:
Output of QA400: 2.85 Vpp 2.3 dBu
Input of mic-pre: ~16.5 mVpp -42.4 dBu
Output of mic-pre: 3.9 Vpp 5.0 dBu
So overall gain looks like it's about +47.4 dB.
The QA400 reports the SNR as 87.4 dB but I think it should be much better than that because I'm attenuating the input stimulus. So is there a way to compute what the SNR is theoretically?
Not that it should matter but here is a pic of the mic-pre and how the QA400 is hooked up: