Become a Site Supporter and Never see Ads again!

Author Topic: Understanding Microphone Preamplifier Noise (link)  (Read 4493 times)

0 Members and 1 Guest are viewing this topic.

Offline huskerdu

  • Trade Count: (1)
  • Taperssection Regular
  • **
  • Posts: 72
  • Gender: Male
Understanding Microphone Preamplifier Noise (link)
« on: January 03, 2018, 07:22:43 PM »
"The main difference between a singer/songwriter and a puppy is that eventually a puppy will quit whining." - Jason Ringenberg

Online voltronic

  • Trade Count: (40)
  • Needs to get out more...
  • *****
  • Posts: 4104
Re: Understanding Microphone Preamplifier Noise (link)
« Reply #1 on: January 03, 2018, 07:43:29 PM »
This is really great, thanks for posting.

The proper measurement technique has been explained here before by Jon and a few others, but it bears repeating.

This bit was news to me:
Quote
The very best EIN that can be achieved is -133 dBV, since this is noise purely from a 150 ohm resistor.

I also see that SD is now listing EIN for the MixPre series in both dBV and dBu.  Previously, they were only using the better-looking dBV figure.
I am hitting my head against the walls, but the walls are giving way.
- Gustav Mahler

Acoustic Recording Techniques
Team Classical
Team Line Audio
Team DPA

Offline DSatz

  • Site Supporter
  • Trade Count: (35)
  • Needs to get out more...
  • *
  • Posts: 3347
  • Gender: Male
Re: Understanding Microphone Preamplifier Noise (link)
« Reply #2 on: January 04, 2018, 09:31:27 AM »
The article recommends using a 150-Ohm resistor as a "surrogate microphone" when measuring preamp noise, and careful matching of gain levels (set with test tones and a meter, not just by ear) when making comparisons. Those are excellent suggestions.

It is indeed completely senseless to judge a preamp by turning its gain all the way up and listening with nothing connected to its input. You will hear differences among different preamps or recorders that way, but that tells you literally nothing about how the preamps will behave with a microphone attached, at gain settings that you would actually use for recording. Really, literally nothing. Don't do it.

What the article doesn't mention, though: Equivalent input noise varies considerably at different gain settings. Perhaps unexpectedly, in most preamps it is lowest at high gain settings--often by a lot. That's why most manufacturers specify it at the maximum gain their preamps offer--generally a far higher setting than one would ever use day-to-day. -- Unfortunately, when you only know the EIN of a preamp at one gain setting, you can't infer anything about its noise at other gain settings. The quieter of two preamps as measured at 60 dB gain (typical for a spec sheet) may not be the quieter of the two at 30 or 35 dB gain (typical for actual recording).

Also not mentioned in the article: Most microphones are significantly noisier than either a 150-Ohm resistor or the input of a good preamp.
  • Complication 1: Microphone noise varies considerably at different frequencies, and so does the ear's sensitivity to that noise. Frequency weighting curves are generally applied in microphone noise measurements--but any such weighting is only appropriate for one particular SPL range. When the noise is at a markedly different level--and in good modern microphones, the noise is 25+ dB lower than the "A" curve was designed for. Thus the weighting curve can skew things enough to produce misleading results.
  • Complication 2: Smooth, steady noise of a given average level is far more tolerable than noise with the same average level but with prominent, momentary "spikes." Some noise measurements, e.g. "CCIR quasi-peak", respect that difference far more than others ("RMS")--guess which figure most manufacturers publish?
Then finally, in live recording environments the same variables occur--frequency and time distribution of the noise--but especially in live, public situations, environmental noise nearly always "swamps" microphone noise.

Thus the search for the quietest preamp can easily become an exercise in misplaced perfectionism (see https://en.wikipedia.org/wiki/Streetlight_effect).

--best regards
« Last Edit: June 01, 2019, 02:02:29 AM by DSatz »
music > microphones > a recorder of some sort

Offline aaronji

  • Site Supporter
  • Trade Count: (9)
  • Needs to get out more...
  • *
  • Posts: 3861
Re: Understanding Microphone Preamplifier Noise (link)
« Reply #3 on: January 09, 2018, 09:21:15 AM »
I also see that SD is now listing EIN for the MixPre series in both dBV and dBu.  Previously, they were only using the better-looking dBV figure.

As long as SD noted the proper units (which they did), I don't see them looking different at all.  Especially since it is such an easy conversion, even for the mathematically-impaired...

Online voltronic

  • Trade Count: (40)
  • Needs to get out more...
  • *****
  • Posts: 4104
Re: Understanding Microphone Preamplifier Noise (link)
« Reply #4 on: January 09, 2018, 07:29:55 PM »
I also see that SD is now listing EIN for the MixPre series in both dBV and dBu.  Previously, they were only using the better-looking dBV figure.

As long as SD noted the proper units (which they did), I don't see them looking different at all.  Especially since it is such an easy conversion, even for the mathematically-impaired...

I agree completely, but there was a bit of a dustup on the GS Remote board accusing SD of engaging in marketing stat-fluffing.  Not worth linking to; it was ridiculous.
I am hitting my head against the walls, but the walls are giving way.
- Gustav Mahler

Acoustic Recording Techniques
Team Classical
Team Line Audio
Team DPA

 

RSS | Mobile
Page created in 0.062 seconds with 33 queries.
© 2002-2024 Taperssection.com
Powered by SMF