Raimund is right here, I have tested tones a number of times and if I
just lean back an inch or move my arm, I can see the level meter change.
I think the clock test is a fine compromise, as long as you can also
hear the ambience.
Looking at the ticks with a software might be really a source for errors.
You have to HEAR something and judge.
Klas.
At 11:13 2007-05-08, you wrote:
>Dan Dugan, you wrote:
>
> > I think that's the weakest point--where a distinction in noise level
> > of perhaps one or two dB is being made, trying to match clock ticks
> > by ear is too chancy for me. I suggest a 1 KHz tone from a speaker
> > between the clocks for level matching, calibrated by measuring
> > voltage at the speaker terminals. You can leave it out of the
> > published movie.
>
>I agree that the short ticks of a clock are probably a bit too
>variable for an exact gain matching of the different recorders.
>
>However, even a 1 kHz sine signal played through a speaker in a more
>or less reverberant room might cause other problems. The delayed
>short-term echoes will produce interferences (superposition) that can
>also lead to relatively high measurement errors.
>
>An even better calibration method would be to bypass the acoustic path
>and to use an electrical reference signal, fed directly into the
>microphone input. In this way, it is also possible to determine the
>absolute input sensitivity (the input clipping level or "gain") of the
>recorder. This is what I did in my tests. I played a synthetic 1 kHz
>sine signal through the head phone output of my (battery-operated)
>Edirol R-09. I measured the rms voltage of that test signal by using a
>common multimeter (435 mVrms =3D -5.03 dBu in my case). I then connected
>the R-09 output with the microphone input of the recorder by using a
>simple voltage divider (two resistors, 100000 and 150 Ohms, providing
>an attenuation of -56,5 dB; the 150 ohms resistor connected to the XLR
>pins 2 and 3). This electrically recorded test signal creates a
>certain dBFS level (for instance -12dBFS) in the recorded .wav files,
>which can be used to normalize the recordings across the various
>recorders.
>
>Nevertheless, I would claim that even a subjective clock tick
>calibration method by ear is probably sufficient for our purposes.
>Yes, it is true that there would be some uncertainty in the range of 1
>or 2 dB. However, such small noise floor differences should be
>irrelevant when using the equipment under real-world conditions in the
>field. For instance, if you managed to half the distance between the
>microphone and the subject, you would improve the signal-to-noise
>ratio by 6 dB.
>
>Therefore, I do believe that the influence of the recorder and even
>the microphone is small compared to the specific circumstances
>(including personal experience, luck and patience) in the field.
>
>Regards,
>Raimund
>
>
>
> > Rob Danielson wrote:
> >
> > >Please do point-out where the method method is lacking...
> > >
> > >The only ear evaluation _I_ do is match playback levels. I make the
> > >high res files available so folks can tweak a test segment up or down
> > >a dB or two to match to their tastes which is quite easy and quick to
> > >do with QT Pro I might add.
> >
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
website: www.telinga.com
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