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Discussion Starter #1
greets,
i've done searches and much reading and finally have succumbed to posting...

i'm stuck on the calibration. i'm running a mac osx 10.4 and i've attempted to calibrate trying two different usb interfaces, the apogee mini me and the m audio duo.

neither of these cards has a software mixer and the volume sliders in the audio/midi section on the mac are grayed out when i select either of them. how does one adjust the input level during calibration? currently i'm getting no input level at all on the meter on the preference calibration page.

on the soundcard page of preferences in the 'output device and output' drop down menu the choices are - default device, md3 mixer and java sound audio engine. for the 'input device and input' the choices are - default device and mac osx core audio audio hardware. regardless of the choice the input volume, output volume and wave volume are always grayed out. what are the correct selections for my set up?

also, please check my understanding of the loop.
my interface is connected by usb to my mac. when i test i will use my digital radio shack spl meter (i've down loaded the correct calibration file and understand this mic is best used on the low end) this mic will be inserted in the right channel of my audio interface.

so the loop must be based on the right channel mic input and the same device's audio output of the right channel. am i correct in removing the mic and plugging the right channel audio output into the right channel mic input of that interface? the thought alone scares the begubbers out of me.

thanks for any help!
raticus
 

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neither of these cards has a software mixer and the volume sliders in the audio/midi section on the mac are grayed out when i select either of them. how does one adjust the input level during calibration? currently i'm getting no input level at all on the meter on the preference calibration page.

on the soundcard page of preferences in the 'output device and output' drop down menu the choices are - default device, md3 mixer and java sound audio engine. for the 'input device and input' the choices are - default device and mac osx core audio audio hardware. regardless of the choice the input volume, output volume and wave volume are always grayed out. what are the correct selections for my set up?
If the cards do not support volume settings then you have no way to adjust them. However, getting no input level suggests a problem with the input selection. For REW you need to set the card you want to use as the default device for both input and output before starting REW, then select "Default device" as input and M3DMixer as output on the REW soundcard preferences.


also, please check my understanding of the loop.
my interface is connected by usb to my mac. when i test i will use my digital radio shack spl meter (i've down loaded the correct calibration file and understand this mic is best used on the low end) this mic will be inserted in the right channel of my audio interface.

so the loop must be based on the right channel mic input and the same device's audio output of the right channel. am i correct in removing the mic and plugging the right channel audio output into the right channel mic input of that interface? the thought alone scares the begubbers out of me.
Bear in mind the SPL meter is a Line-level output, it should be connected to a line input. For the loopback you do connect the right channel line out to the right channel line in.

If you are using a PowerPC Mac you may need to select the "Force big-endian output" box, to check that open the REW signal generator and play a 1kHz sine wave, if you hear a pure tone all is well, if it sounds like a buzz saw tick the Force Big-endian output box and it should change to a pure tone. That needs to be done before trying to calibrate the soundcard.
 

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Discussion Starter #3
john,
thanks for your quick reply. there is nothing more stress relieving than waking up to a post full of helpful facts.... on a sunday no less.

i walked thru all your instructions (card selection before opening rew - check, sine wave - check, sound card prefs - check), and couldn't get a signal. undaunted, i moved on....

i picked up a suggestion from another post that involved using the mac's soundcard. light bulb..... i hooked up the loop and it all worked the first time. i'll take it.

so, the mac sound card is an acceptable option?
and is the roll off on the chart, starting around 200hz down to 20hz, a concern?

thanks for being there,
raticus
 

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The Mac's own soundcard is fine, no problem to use that. Not sure about the roll off, please post a screenshot (use the camera icon top left of the graph to capture the graph image and attach it to your post).
 

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Discussion Starter #5
test.jpg

here's the graph.


for the looping signal chain i used a stereo cable to connect the headphone output to the audio input, and then just turned the left channel down all the way in the audio/midi utility. is that ok? the little details are the ones that always get me.

raticus
 

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A stereo loopback is fine, no need to turn down the other channel, REW just ignores it. The loopback result is reaching -3dB at 20Hz, which isn't a problem - just bear in mind that anything below 10Hz or so will be noise rather than reliable data.
 
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