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Re: Equipment Testing Goals Methods

Subject: Re: Equipment Testing Goals Methods
From: "Klas Strandberg" klasstrandberg
Date: Tue May 8, 2007 7:44 am ((PDT))
I can add:

The normal ear is VERY sensitive! 20 years ago, with cassette
recorders!!! I made various "dummy-head" recordings and had people
listening. I asked strange questions like: Is this recording made
above a road or grass? Is this recording made inside my balcony or outside?
People could give good answers.
I made a recording at the top of the dome-church here in Uppsala. One
person who was very afraid of highs, got anxiety without knowing
where the recording was made.
Another got vague feelings of being sea sick, without knowing that
the recording was made in a rowing boat. etc.

So hearing the ticks and the ambience is a reasonably good way, I
think. The ear will discover important errors.

Klas.



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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