After posting several queries in my previous ECM-8000 thread, & getting satisfactory answers to them, I finally went in for the Xenyx 302 USB mixer

http://www.behringer.com/EN/Products/302USB.aspx

The ECM-8000 connects to the XLR input of the mixer, (which finally proved to be Phantom Powered), & the mixer is connected to the Computer through a USB cable. So collectively this is like making the ECM-8000 a USB mic. Though the Xenyx does not seem to be full-duplex (at least from what I've read so far), the USB port can be used either as an Input or as an Output, but not both together. If I had to configure it in such a way that it's mainly used to convert the Mic into USB (line-level Ofcourse), I would still need to use the onboard soundcard of the computer to output the sweeps to the amplifier. In this case, I see no use of a Soundcard Calibration file needed, because the input becomes USB & output is that of the soundcard itself, & there does not arise a situation of a loopback connection to calibrate. Or am I mistaken...???

You are experiencing a quandry of duality my friend. If the input is the mixer, and the output is the soundcard, then it makes sense to route the soundcard out to the mixer in. The soundcard out is measured through the mixer in, and both transfer functions will be represented in the recording. The only thing to concern yourself with is any feedback that may occur from the mixer being routed to the soundcard output. Also make sure to turn off the phantom power when routing in the soundcard.

Well if it gets complicated that way, then I might as well skip the USB connection ( for signals) & take the line-out of the mixer to feed the line-in of the computer soundcard. So this way the set-up gets at the default style. And may be just power up the mixer via USB...

No no no, there is no need to use the soundcard inputs. The mixer is the INPUT. The soundcard is the OUTPUT.

One thing that using two digital sources presents, is internal OS routings. The output must be the soundcard and the input the mixer. If you cannot set up your program to use these I/Os exactly, it may be a driver limitation. Make sure you are using ASIO for both devices. You can use ASIO4ALL if the soundcard doesn't have an ASIO driver. In this case, I think you also use ASIO4ALL for the mixer as well.

If you cannot figure this out, post some screenshots of your configuration programs and we can help further.

But even in that case, a soundcard calibration file is not possible (or needed) correct??

The .cal file is required for the most accurate result. There are two devices the signal must pass through and they are not to be considered as part of the acoustic system. In reality, the output device will be part of the system, but you cannot loopback to measure the output only.

You have to make it possible for your measuring program to use the soundcard as out and mixer as in. Refer to my last post. If you cannot make that happen, then I don't know what you can do if the mic requires phantom power. You might have to resort to a DI box.

So the bottom line is that the .cal file doesn't come into the scene here..??

To sum it all up, the sequence goes
Like:-

REW (sweep) =>Soundcard Out=>passing through amp/speaker=>ECM-8000=>Mixer XLR in=>USB OUT of mixer=>USB IN of the computer=> back into REW

Since the input of the soundcard is not used here, there does not arise a situation to calculate the input/output differential (calibration) of the soundcard. I'm curious if this is the case with all USB Mics--

I'm sorry if that's what u tried to say

In all honesty, an audio interface that is not full-duplex is not worth the cost. You really should consider an alternative product. Think of this: almost every other USB product is full-duplex.

Where the soundcard out is, you bypass the speakers and mic, and connect a cable directly to the mixer in.

You really should consider returning the mixer. Not having FULL I/O is rather useless.

I always create a cal file but my understanding is it really is not all that important when doing A/B testing. If that is the only thing stopping you then I would skip it and move forward with testing.

The question of being full-duplex or not arises ONLY when I route the signal through the USB port. As mentioned earlier, I can still skip the USB part & route it the default way as mentioned in the connection diagram here:-



The diagram has been shown using the xenyx 802.. It's exactly the same as my 302 except that the 302 has USB *ALSO*

WHY would I opt to connect the soundcard Out to the input of the Mixer???? I am using the mixer ONLY to get Phantom power. The soundcard out is better off going straight into the Amplifier. What's the benefit of passing it through the Mixer again..???

I am not familiar with the ECM8000, but if you are saying it has a USB interface for the mic exclusively, I would opt not to use it, rather use it as input to the pre on the mixer.

Thanks Glenn. As I mentioned earlier, I sure can make a loopback between the in/out of my soundcard & Create the cal file, but in my case where the soundcard input is not used, I guess it would only make things worse to use the cal file... Correct me if I'm wrong

...because this is how the loopback calibration is done.

How are you using the mixer for phantom power, while at the same time not using it for the preamp and ADC?

The ECM-8000 has only an XLR output. The MIXER has both USB & line level outputs. If I close an eye on the USB side, it's just another Mic preamp, which is exactly what's shown in that diagram...

Okay, the diagram shows using the mixer unit as preamp only. This is useless because it should be able to convert analog to digital, where it would appear as an input source in your OS. Doing it the way illustrated is losing fidelity of the preamp, because the soundcard might have a poor ADC.

Still, in this case you loopback a cable from the soundcard out to the preamp in. Then calibrate.

Lol. Either of us as getting confused here. I hope it's not Me
A loopback connection is made only to ascertain any differential between the inputs & outputs of a particular soundcard. And repeating it all over again, when I'm not using the input of the soundcard, where does the question arise of a loopback??
As far as my knowledge goes, it's done to ascertain any flaws in the frequency response of a soundcard's INPUT section Vs its OUTPUT section. And here the soundcard is only used for Output..

That's exactly what I've been trying to say
The loopback arises only when I use it as mentioned in the diagram, where BOTH the inputs AND outputs of the same card are being used..
Not the same when using USB as the input...

You were just detailing using TWO preamps as input.

Why would the Mixer do any ADC??? It naturally is done inside the soundcard. The Mixer is just Boosting the microphone signal & outputting analogue. So where does a Mic Preamp ( Mixer in this case) come into the area of ADC???
The diagram is clear & straightforward ..

There is still a loopback no matter what diagram you use.

Huh??? No way !! Look at my original post...

Is it?? Lol

Yes. The calibration is to offset the irregularity of the preamps and DAC/ADC.

Correct. When measuring differences only, a linear system will present no errors.

In that case, please enlighten me as to how the connections have to be made in my case before I press the "Make Cal" button..

If your input has a TS socket, then you can use a 1/4" cable. Your soundcard out most likely has a 1/8" TS. In this case, you can use a cable that is TS 1/8" to 1/4" mono.

What goes where???

Does a round peg fit in a square hole?