Hi fons, you're 'fons' in jack-devel, aren't you? Thanks =) On Thu, 2009-11-26 at 11:50 +0100, fons@xxxxxxxxxxxxxxx wrote: > On Thu, Nov 26, 2009 at 05:07:16PM +0800, Ng Oon-Ee wrote: > > > Sorry to sound like a broken record, but could anyone with knowledge in > > these matters advise me on:- > > > > 1) How much gain is needed by the Shure SM57 for comfortable recording > > with a low noise floor? > > 2) Whether the M-Audio Fast Track Pro, Tascam US-144, Alesis IO|2 or > > Edirol UA-4FX are able to provide pre-amping with that much gain? > > The question to ask is not how much gain would be required. > All these interfaces will provide enough gain to the point > that increasing it will not improve S/N ratio. > > The important question is then: how much noise do we have > in those conditions ? > > Two values are important for this : the self noise of the mic, > and the equivalent input noise of the preamp. > > For the SM57 the self noise is easy to find: > > Sensitivity = 1.9 mV/Pa or -54 dBV/Pa > The reference sound level is -94 dBPa, so the > mic will produce -148 dBV at that level. > > The SM57 is a passive microphone, so its self noise > is determined by its impedance which is 310 ohm. > This will produce a noise voltage of around -130 dBV > in the audio range. > > Comparing these two numbers, the result is that the mic > will produce the equivalent of around 18 dB of acoustic > noise. For example if you record a sound of 78 dB SPL, > the S/N ratio will be 60 dB. > > This is a typical figure for a mic of this type, which > is not really designed for low-noise use such as recording > classical music or soft instruments. It's used mainly for > solist voice, amplified instruments and drums. The best > low-noise mics would be some 10 dB lower. > > > The second parameter, equivalent input noise, is the > noise of a preamp, measured in some operational condition, > and assuming all that noise is generated by adding it at > the input. For a good preamp this will be very close to > reality. It will have the best EIN at max gain, and this > level will remain almost constant over a large gain range. > > None of the four manufacturers provide this information, > nor any other data from which it could be computed. This > is no coincidence: for most 'consumer' type preamps the > EIN is not very good, and manufacturers want to avoid > that you compare their performance to the competition. > > For my Edirol UA-5 I just measured it. For a source (mic) > impedance of 150 ohm it is around -120 dBV, at 310 ohm > it would probably be around -117 dBV. Now if you compare > this to the self noise of the mic, -130 dBV, the conclusion > is that the preamp will produce 13 dB more noise than the > mic. Not very good, but quite typical for any product in > this price range. > > Combining all this, using the SM57 with the Edirol UA-5 > would produce a noise level that is equivalent to 31 dB > of acoustic noise. This is, in the end, the only figure > that matters, as it determines what you can record with > a good S/N ratio and what not. > > HTH, > Thanks for the good write-up. As you mentioned, where I was frustrated is the lack of information from manufacturers. I guess the old adage that 'you get what you pay for' is, in the end, true. I gather, then, that I should be seeking information comparing the ADCs of the cards I listed, probably from side-by-side reviews. Prices are competitive with each other (from 139 USD to 190 USD) and within my budget, barely. Thanks for the help, again. _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
