Topic: Noise pattern in a recording, using PCM-D50 and SP BMC 2

[nzo]

Hi all,

I'm getting some low frequency noise using SP BMC 2 plugged directly (no battery
box) into PCM-D50, when recording in concert venues.

Here's a sample:
http://rapidshare.com/files/216715266/noise.mp3

Looking at the waveform in Audacity, I'm seeing clicks every 12 ms, so
noise frequency is around 80Hz.

Now, when I test at home, everything is perfect, no noise.  So it has to be in the
concert venue.  During the concerts, I did not notice any low freq noise, so I'm not
sure what the PCM-D50 is picking up.  I don't think this is from cell phones, but I
was wondering if this could be caused from the systems concert venues use to stop
cell phone signals.

Interestingly, with my Edirol R-1, in the same venues, I did not notice anything, but
looking at the signal during silences, the preamp of the R-1 might have masked this low
noise (or maybe the R-1 has a filter ?).

What do you think ?  Also, what is the best way to handle such noise, is it better
to filter it when recording (the PCM-D50 can be set to cut low freq, I think less than
150Hz), or to do it in post-processing ?

Thanks for your help,

[digifish_music]

I can tell you the noise is at 83.3333 Hz (12 ms), with a period of 41.6666 Hz peak to peak (24 ms), given there seems to be a positive and negative spike.

Sounds and looks like some sort of digi-noise or related to the mains power? Dimmers on the lights, flouros? transformers?

I have had similar issues with SP-TFB-2 mics picking up noise from an R09 btw.

EDIT: It's interesting that 12ms period divides evenly into 44100 Hz (3675x) ...probably then something to do with the mics picing up digi-noise from the D50

digifish

[rjp]

I have had similar issues with SP-TFB-2 mics picking up noise from an R09 btw.

I have also had trouble with the SP-TFB-2 (and other external electrets) picking up ~352 Hz diginoise from an LS-10 - I have to be very careful about orienting the cables and making sure that the recorder's LCD is pointing away from my body, OR that I'm holding the recorder in my hand (body contact eliminates the hum).

[nzo]

that I'm holding the recorder in my hand (body contact eliminates the hum).

That might be it !   In my tests at home, I was holding the recorder (no need to be stealth...)
I guess I'll have to do more tests, and experiment with an ESD wrist strap  !

Will keep the group posted about my results, thanks a lot for your answers.

Also, since I just received my 16gb memory stick, I'll experiment with 24 bits/96 khz,
and see if I can figure how the noise is correlated to the sampling frequency.

[digifish_music]

that I'm holding the recorder in my hand (body contact eliminates the hum).

That might be it !   In my tests at home, I was holding the recorder (no need to be stealth...)
I guess I'll have to do more tests, and experiment with an ESD wrist strap  !

I can confirm that holding the recorder is a bad idea with the R09 and SP mics for noise. 

digifish

[nzo]

I will experience:
- wrapping the PCM-D50 in an ESD bag, and add some aluminum
foil around to build a ghetto Faraday cage (and as soon as I
receive the copper foil I just ordered, replace the Alu foil with it),
- put a ferrite core on the SP BMC 2 cable
- (maybe buy some snake oil too ?)

The Faraday wrapper might seem very inconvenient, since there's
no easy way to check the levels, but in my case it's not a big issue,
classical music concerts have more or less the same loudness.

I will report my results soon !

[Dave_Scream]

I will report my results soon !

Why you did not report your results?
I bought today Sone M-10 + Soundprofessionals MS-TFB-2.

[nzo]

Hi Dave,

I did not quite reach a solution unfortunately with that setup (though the ferrite core helped somewhat).
Also, I found anyway the SP-BMC2 were a bit noisy for my use (classical music venues), so I looked round and
eventually bought and modded Shure WL-183 microphones,  The cable on these seems much sturdier (so might be
better shielded), and the issue I described never appeared again.

Hope you like your M10 and SP-BMC2!

Laurent