Thanks Fons. This is exactly the kind of input we need.
I ran an equivalent input noise test on the Zoom F8 last night, in the standard manner of soldering a 150 Ohm resistor across pins 2 and 3 of an XLR, for a dummy load. I can confirm relationship between input gain and mic pre noise floor is absolutely linear between 55dB and 75dB of gain. I.e when you drop the gain 5dB, the noise floor also drops 5dB. The relationships deteriorated by 1/3dB or so between 50dB and 40dB. Below 40dB gain the EIN performance deteriorates more severely. I will update the doc in the gdrive folder to include a graph of this behaviour. 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. At 58dB gain, the noise floors are 27dB apart, which is a considerable improvement, indicating that Tetramic and Zoom F8 owners, of which I imagine there are far more than tetramic and Millenia HV3 owners, should ensure they set their gains above 50dB to ensure best noise performance. Using a Millenia pre, with 6dB better EIN than the F8 would be a further improvement. I will therefore use the 58dB tetramic recording as a more fair comparison in the test. 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. Thanks again for your input. This is the sort of discussion I hoped this study would produce. It’s easy to prove things one way or another when you have a starting point to work from. Just for the record, and for transparency, am I right in thinking you work closely with Len Moskowitz and CoreSound on the development of the Tetra VST A format to B Format encoder and calibration method? Cheers Jack Sent from my iPhone > On 3 Nov 2023, at 20:17, Fons Adriaensen <f...@linuxaudio.org> wrote: > > On Fri, Nov 03, 2023 at 12:34:52PM +0000, Jack Reynolds wrote: > >> I think the point here is we tested at two different pre-amps >> gains, to eliminate that as a potential source of noise. >> There was no difference in SNR, indicating the noise is generated >> by the capsules and electronics, and not the preamp. > > Not having the required info (see below), I can't claim that the > conclusion is wrong. But the reasoning behind it certainly is. > > The Zoom F8 preamps have an EIN of -127 dBu(A) at maximum gain. > Not bad, but not exceptional either. And that is the only spec > we have regarding EIN. > > It says NOTHING about EIN at other gain settings, in particular > much lower ones. > > A well designed mic preamp will have its best EIN at the highest > gain, and stay close to that value for a range of 15-20 dB below > maximum gain. But for some the EIN will rise as soom as gain goes > down. > > As an example, have a look at > > <http://kokkinizita.linuxaudio.org/linuxaudio/einslide/ein.pdf> > > This compares the measured EIN of two 8-channel preamps: the Aphex > 1788A and the Behringer Pro8, as a function of real gain. > > At maximum gain the cheap Pro 8 ($200), is actually better than > the Aphex ($4000). But not for long as gain is reduced. > > The 65 dB gain range of the F8 is probably a combination of > passive attenuation, real analog gain, and (maybe) some > 'digital gain' as well. It's nowhere documented. > > The gain used for the recordings was 38 dB, that is 37 dB > below maximum. The real EIN at that setting is anybody's > guess. Until it is actually measured, we just don't know. > Even with 20 dB more gain, that is still 17 dB below max. > > Making all the recordings at the same gain setting just > doesn't make any sense. The correct way to do this is > to use a sensible gain setting for each mic, and document > that. > > The available recordings do not include the raw (A-format) > one for the Octomic with additional gain, and the Ambix > ones do not have the 71 dB(SPL) noise signal. So there is > no way to really compare them to anything else. > > Ciao, > > -- > 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. _______________________________________________ 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.
