why does my microphone calibration file look like this

[bwana]

Picture 1.jpg

it seems to get noisier at the higher frequencies
equipment
macbook
rew (latest version)
mic behringer ecm 8000
preamp maudio fast track pro

i also tried to make adjustments in the
Applications>Utilities>Audio Midi Setup application but there are restrictions.
Even when i set all the drop down menus for the fast track pro (input,output,properties),
I cannot configure the Audio Input or output sections much.
I can set source and format for audio input and only format for audio output.
I cannot set levels. Is this because thesignal is digital from the laptop
and the actual analog parameters are set in the maudio box?

[brucek]

The microphone calibration file is simply a file of values loaded in REW to compensate for mic inaccuracies. There's no measuring involved.
The ECM8000 mic has a calibration file we provide on the download page.

Can you explain what you're doing - I'm confused?

brucek

[bwana]

i am following the 'getting started' instructions for REW.
First get a loopback cable. In my case it goes from the RCA output on the back of the maudio fast track pro to a TS jack that fits into the combo jack on the front of the maudio fast track pro.
Then i go to settings and start with the sound card calibration. The first step is setting the level. I do this by adjusting the knob on the front of the maudio box so that the measured level matches the output level in the little vu meter bars.
Then i hit calibrate and the thing gives me a curve which sort of looks like the thing i posted but rolls off at the high (>20khz). What bothers me is how the 'noise' (jiggliness?) increases during the frequency sweep.

[brucek]

Then i go to settings and start with the sound card calibration

So this is a soundcard calibration you're having trouble with and not a microphone calibration as your thread title indicates?

If that's a soundcard calibration response chart you've posted, I would say you're not getting any signal over the loop.
Are you selecting the correct channel in REW as you are using for the loopback cable - right channel ?

brucek

[bwana]

sorry, yes, this is a soundcard calibration.

yes, the loopback cable is properly inserted. when i intentionally select the wrong channel, the db is much lower, i cannot match it to the output signal on the vu meter that pops up, and the program warns me that the level is too low if i try to calibrate. have you ever seen such a problem before?

[brucek]

Did you select the RCA output that your cable is plugged into on the back of the unit (1/2) or (3/4)?

I see the switch that toggles between line and mic. Did you set it for line?

Instrument/Line Selector Button (Inst/Line) – This button selects the input level of the front panel 1⁄4” inputs. In the out position,
the inputs are set to accept an instrument level signal (such as that from a guitar or bass) while in the in position they are set to
accept a line level input (such as that from a keyboard or drum machine). Please note that the XLR input level is unaffected by
this switch.

brucek

[bwana]

i repeated the same process on a windows machine (in fact it ws the same macbook booted into windows) and without changing anything on the fasttrack pro-here is the result
sndcrd cal.jpg

this is the expected graph. obviously the mac os (leopard) is not handling things properly.

and btw, flipping that little switch does not change the result-same curve is obtained.

[brucek]

That's what it is supposed to look like. Save it..............

brucek