Older cal file?

[i5rast]

I've got an older sample of the ECM8000, from 2003 I think. I guess that means it has got the Panasonic WM-60 capsule. Is there any way of getting hold of a reasonably accurate cal file for this older version?

[brucek]

Appears no one has a file for that capsule.

I suppose you could get it calibrated.

brucek

[i5rast]

Thanks for your reply, brucek. Hard to know which version the graph in Behringers spec sheet is supposed to be for, old or new capsule? I asked them but got the most informationless answer one could imagine. Do you think it would make any sense to use the newest cal file available here? I have no idea how different the new copies of ECM8000 are from what I've got.

Also I have been thinking about the difference between analogue and digital soundcard outputs: aren't the sine waves etc. used in REW digitally generated, so that the digital S/PDIF output from any soundcard will be near perfect in its frequency response? That would leave the input's deviations from the ideal to consider. What if that one is digital/USB too? Of course that means the A/D conversion took place outside of the computer, but since the mic preamp is not included in the regular soundcard cal files/loops with REW anyway, it would make no difference compared to using analogue I/O with cal file, right?

[brucek]

Do you think it would make any sense to use the newest cal file available here?

I really can't say. I don't know exactly when Behringer changed their ECM8000 capsule, and don't know if it's really much different than the present one.

the digital S/PDIF output from any soundcard will be near perfect in its frequency response? That would leave the input's deviations from the ideal to consider. What if that one is digital/USB too? Of course that means the A/D conversion took place outside of the computer, but since the mic preamp is not included in the regular soundcard cal files/loops with REW anyway, it would make no difference compared to using analogue I/O with cal file, right?

A few points to consider.

Yes, the digital output of a soundcard can be quite good, or it may indeed not be so good, but you have the input problem from an analog microphone to consider.

When you use both analog line-output and analog line-input to a soundcard with REW, you pass that entire loop through a calibration routine that renders the results of measurements made with those same ports near perfect down to 2Hz. What more do you want from a measuring device? This allows you to use an inexpensive soundcard and get steller results. Why mess with digital, when analog is perfect. REW was designed to be used with analog.

If you use the soundcard cal file method rather than the Left Channel loopback method, then you have the advantage of including the inadequacies of your mic preamp in the correction file. Where you normally would use a straight cable from line-out to line-in to create the soundcard cal file, you include your preamp inside that loop and then create that file, so the soundcard file compensates for both the soundcard and preamp.

brucek

[i5rast]

Thank you for that, interesting. I was not quite aware of the possibility of including the preamp in the measurement loop when creating a soundcard cal file. I thought maybe the line out level would be too high for feeding into the mic preamp, causing clipping/distortion? But I take your word for it, very appealing to include the preamp frequency response imperfections as well!

[brucek]

very appealing to include the preamp frequency response imperfections as well

I thought so, and included my XENXY 802 preamp in my cal file for a while and then did some testing with and without that postion baked into the file, and found it didn't really matter that much to the response of my system. A dB or two is about all it mattered. Not really enough for me to care about..

It all depends of course, on the response of the preamp itself. Easy to determine by using your regular soundcard cal file and then take a response measure of your preamp. You'll know then if it's worthwhile.

brucek

[i5rast]

Maybe this is a silly question, but did you then actually plug the line out from your soundcard into the mic input of your XENYX? Or did you rather use the regular line in of the XENYX, assuming the response would be approximately identical to the response of the mic input? I am just a bit hung up on the idea that the line out level will be far too high and cause clipping at the mic input.

[brucek]

I used the line-level input and line-level output of the XENYX, and so yes it bypasses the first stage of the device. If I had balanced out from my soundcard, there's no reason I couldn't use the mic level input though, since there would be complete control of the signal level (to avoid clipping as you say).

I don't thing bypassing that single stage is too significant. Certainly the response of the XENYX is extremely good from line-in to line-out. So good that I don't use the soundcard cal method anymore, rather preferring the Left Channel cal.

It doesn't hurt though, to check your preamp response to be sure that it isn't adding too much inaccuracy. Be sure that you verify that a single looped back cable returns a perfect flat response and then insert the tesing device into the loop and set up the levels and measure.

brucek