Hello Raimund,
most important is that you have measured the same way all the time. I am
very grateful for your work over the years.
Klas / Telinga
On 2019-03-20 13:51, [naturerecordists] wrote:
>
>
> In order to finally get absolute signal levels I use a common function
> generator that is setup to provide a 1 kHz sine wave at a signal level
> of 1.09 Vpp, which is equal to -6 dBu (one could also use another
> field recorder or a computer soundcard if the exact output signal
> level is known - a common multimeter for instance would allow to
> measure that level).
>
>
> I connect the microphone input to the output of the function generator
> through a home-made 56.5 dB attenuator, which means that the signal
> level at the microphone input is -62.5 dBu. I record this signal for a
> few seconds at the maximum gain setting of the recorder. I then
> disconnect this reference signal and terminate the microphone input
> using a 150 ohms resistor and record this silence (the inherent noise
> floor) as well at the maximum gain setting.
>
>
> In the analysis software (I use Avisoft-SASLab Pro) I first band-pass
> filter the recorded .wav file from 50 to 18 kHz and calibrate it based
> on the recorded -62.5 dBu reference signal using the calibration tool
> of the software. I then measure the rms of the noise signal, which
> provides the unweighted EIN value. If the frequency spectrum of the
> noise floor is flat, I subtract 2.1 dB from the unweighted EIN to get
> the A-weighted EIN.
>
>
> One can also use other software that can calculate rms values
> (including the free Avisoft-SASLab Lite software for instance, which
> does however not allow direct calibration). You just had to subtract
> the rms [in dBFS units] of the reference signal from the rms [dBFS] of
> the noise level and add the absolute signal level [dBu] of the
> reference signal used.
>
>
> Regards,
>
> Raimund
>
>
>
>
>
|