On Sat, Nov 04, 2023 at 08:53:57AM +0000, Jack Reynolds wrote: > The noise floor of the F8 mic pre is about about 10dB below the > noise floor of a single tetramic capsule at 38dB gain at 1KHz.
How do you arrive at this figure ? > I also need to repeat the test with an 80 Ohm resistor load for > a more accurate comparison with the Tetramic as the lower output > impedance may have an effect on the noise floor at lower gains. At lower gains it won't have any effect. At higher gains there may be some difference, but it will be small. Anyway the 'standard' source impedance for an EIN measurement is 150 Ohm. Note that to find the real EIN, you also need to know the actual gain of the preamp. That means you need to know the exact relation between the analog input level and the digital level after the A/D converter since the latter is the one you actually measure. The nomimal gain (10 to 75 dB on the F8) doesn't have any meaning, not even if it happens to be the actual analog gain up the input of the A/D converter. The only 'gain' value that has real significance is the inverse of the input level that results in a full scale digital signal i.e. minus the X axis values in the example graph (which uses dBV on both axes - I should have mentioned this). Measuring that in a reliable way is not as easy as one could imagine, there are lots of ways to get it wrong without being aware of that. -- FA _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
