AFMG Network Forum

alliaphagist · Member

I am a new Easera user, and I have a few questions about calibrations. I would like to be able to use a reference file to compensate for the frequency response of my measurement microphone, a Goldline TEF04. I have a print-out of the frequency response that was provided from the manufacturer, and I was hoping for a way to create a reference file by manually entering values for different frequencies. It seems that reference files are supposed to be audio files, and I'm unsure of how to create or obtain one for my microphone. Similarly, how could I create a reference file for a loudspeaker for frequency response compensation?

Also, am I correct in my understanding that complete input calibration requires both acoustic and electronic calibrations, while output calibration requires only electronic?

Thank you,

Benjamin Russo
Applied Research Laboratories
The Pennsylvania State University

Charlie · Member

Hi Benjamin,
If you want to compensate for the acoustic response of a microphone or a loudspeaker you will need an acoustic measurement of the device as well as that of something to reference it to; say a reference microphone or a reference loudspeaker. If you have a good quality measurement microphone you can use this as the reference for your TEF04. If not, you may be able to have Gold Line email your the TDS file from the measurement they made and printed which was included withe the mic. This can then be used to create the compensation file in EASERA.

I believe there is a pretty good description of how create compensation files in the EASERA on-line help/manual. Give it a try and if you have problems post back with specific questions. There are quite a few good folks that monitor this forum that will chime in to assist.

alliaphagist · Member

Thanks for the reply. The only information I could find in the tutorial or help files was about creating a hardware reference. I guess I'm a bit confused about why a reference file is supposed to be an audio file, i.e. with a time axis. I would think that to represent the frequency response of a loudspeaker, I would just need a single sample frequency plot.

Charlie · Member

Hi Benjamin,
The reference file must fully compensate for a particular device. As such, a transfer function or impulse response (IR) measurement of the device is needed. The frequency response you mentioned will work if it contains complex data, i.e. phase. An inverse FFT may be applied to this data to yield an IR with a time axis as opposed to a freq axis.

A transfer function (frequency domain) and an impulse response (time domain) are just different views of the same event or data. One does not have any different data than the other. It is just displayed differently.

alliaphagist · Member

Thanks--I just had a lapse trying to get my head around that I guess. Do you (or anyone else) know if it's possible to somehow use the information in an EASE loudspeaker file to create an impulse response to use as a reference in EASERA? Otherwise I suppose I would have to measure it myself in an anechoic chamber?

edit: changed second EASE to EASERA

Bruce · Member

Hi Benjamin,
You should be able to measure this yourself by either doing a ground plane measurement, or measuring the loudspeaker in a large enough space with EASERA. You are just interested in the direct sound, so window out any reflections. Just be aware of any low frequency restrictions created by the windowing.

alliaphagist · Member

Thanks Bruce. So there's no way to have .spk file information used as a reference in EASERA? No sequence of exporting and importing?

Charlie · Member

Hi Benjamin,
The answer is no for two reasons. First, the data in an SPK file is relatively low resolution at 1/3 octave. This is not suitable for use as a reference. Second, there is no guarantee that the data in an SPK file, or any other measurement, is identical to the device for which you seek a reference. The actual device should be measured and not some other unit of the same make and model.

AFMG Pedro Lima · Forum Moderator

Hello all,

a reference for the loudspeaker seems not to be problematic. But, how can I create a reference file for the microphone? I see that I waste $50 by buying the microphone reference from Earthworks (wich only comes with the frequency compensation).
Can you guys indicate some papers or some tutorials on how to do that?

Thanks in advance,
Pedro