Calibrate Sound-Card Question

I have been watching YouTube guides on how to use REW, but these have not been helpful. To calibrate my sound-card I am instructed to connect the output of my interface to the input of my interface. What interfaces? This is wholly unclear to me.

I have a Mac Pro 5,1 Tower computer running Monterey macOS 12.7.3. However, I do not use the sound-card on my computer, but have peripheral devices for DAC and ADC, as follows:

INPUT: I use the RODE NT1-A microphone to that goes via balanced cable to the Audient iD4 mixer, a USB device. I have calibrations files for this microphone.

OUTPUT: I use the digital optical output to a Schiit DAC Modi box, connected directly to the Schiit Magni headphone preamplifier, which in turn is connected to the AUX input on the Yamaha R-N301 Stereo amplifier, that is driving Jamo S629 HiFi speakers. These speakers have subwoofers on each channel.

This system bypasses the Apple Mac Pro built-in sound card. The Mac Pro is used only for digital processing of audio files.

What must I connect to what in order to make the "sound-card" (peripheral devices) calibration file?

Hello Wayne,
Thank you for your suggestion.

sm52 said:

To calibrate a sound card, the output and input must be on that sound card. But you have an output on one device and an input on another. Also, there should be 2 outputs and inputs. iD4 has two outputs, but one input. There is also an instrumental input. But it doesn't seem to fit. For your purposes, it seems to me that calibrating the sound card is not necessary. Try measuring without calibration. Use acoustic synchronization for measurements.

Click to expand...

Thanks for the suggestion.
I am a rank beginner, and do not know what acoustic synchronisation means. However, I am sure that my system (the Audient and Schiit boxes) must be imparting some distortion to the input and output. You can think of this setup as an external sound-card. Without calibration these artifacts will not be corrected. I am awaiting a cable that will permit me to create this loop, and I will try that first.

Wayne A. Pflughaupt said:

The interface is the device that the measurement mic plugs into (typically requiring phantom power), with its output going to the sound system. I’d say the Audient performs that function in your system, but I’m not entirely understanding your connection scheme; I can’t find anything showing the iD4 with a digital output.

Regardless, REW’s calibration routine requires an analog output – it can’t be done with a digital output.

The main purpose of the calibration routine is to provide a timing reference for certain acoustics measurements. If your objective is frequency response measurements, you can skip that step.

Regards,
Wayne

Click to expand...

Hello Wayne,
Thank you for your suggestion.
The Audient iD4 Mark II uses the USB-C to get power and to send a digital audio signal to the computer. It is also possible to use it as the output, and use the iD4 as a preamplifier for the speaker outputs.
I am following this instructional video, recommended by REW.


Go to "Calibrate your Sound Card" at 3:12 in the video.
If I understand correctly, I will need to take the Schiit headphone preamplifier output (AUX unbalanced) and feed it into the audient microphone input (balanced) to do the test. I have just placed an order with Thomann.de for the Cordial CFU cable to make the loop. I hope this does not immediately start a screaming feedback loop.
I am sure that my system (the Audient and Schiit boxes) must be imparting some distortion to the input and output. You can think of this setup as an external sound-card. Without calibration these artifacts will not be corrected. So, I should calibrate the setup. If this is not what I should do, please let me know.
I want to time the resonance in my listening room. I am retired and have recently downsized to an apartment with concrete walls on all sides, concrete floor and concrete ceiling. The acoustics of the small living room is horrendous. I want to record the room resonance, including the waterfall diagrams, and keep before/after treatment measurements. The room treatements will include bookcases, absorbtion panels and a diffuser wall.

Wayne A. Pflughaupt said:

I can see why the interface calibration is difficult to figure out in that video, due to the strange connection scheme (pigtail cables) of the unit used.

Click to expand...

Indeed. I found it confusing.

Wayne A. Pflughaupt said:

BTW, the video is incorrect – the soundcard calibration cannot address or correct distortion. If the interface has poor distortion characteristics, it is what it is – there’s no fixing that. Getting a different interface is the only option.

Click to expand...

I know that the calibration of the sound card does not correct the sound card, but when measuring room effects it will removed the sound card characteristics from the room effects that have been measured.

Wayne A. Pflughaupt said:

Any particular reason why you feel that way? Is this something you’re actually hearing? I ask because the published specs for these two pieces is absolutely stellar, to the point that even if exaggerated, they would still be excellent.

Click to expand...

Yes, they are excellent: Both Schiit boxes and the Audient iD4. Even if I assume that they are close to perfect, the calibration step is nevertheless required by REW. As these comprise my external sound card, any colouration of the signals imposed on the test signals out-going and the microphone signals in-coming can be subtracted from the test results. There won't be much to subtract, but apparently this step is required.

Wayne A. Pflughaupt said:

In that case, I suggest simplifying things for the purposes of the measurements. The headphone rig in the signal chain is not necessary for what you’re trying to accomplish, and it’s really just cluttering up the process.
Just use the Audient: Mic in, analog output to the Yamaha amp and speakers, USB to computer. Do the loopback connection for the Audient to get your timing reference and measure away. You can add the headphone rig back in after you’re satisfied with you treatments and the measured results.

Click to expand...

I have found that the output of the DAC is ±1 Volt, which is too much for the amplifier. The Schiit Magni box has two outputs, one on the front for a headphone, and tulip connectors on the back for the AUX outpu that is ±0.3 Volt, which matches the AUX input of the Yamaha amplifier. I must leave the headphone box in the system. My son has an identical computer and sound rig with these differences. He does not have the Modi headphone preamplifier. Instead he uses a Denon amplifier to Denon speakers, and employes the headphone jack on the front of the Denon amplifier. We had the same problem with the Schiit DAC giving a signal at a level too high for the Denon amplifier, so we put the Schiit Sys Passive Box into the circuit to bring the signal down to ±0.3 Volt (at the recommendation of Schiit), which worked perfectly. So, I shall leave my headphone box in the circuit.

I am sure your suggestion to go directly from the RODE Microphone -> Audient -> Yamaha Amp -> Jamo Speakers is wrong. Why would I do this? It bypasses the computer and will give a feedback squeal. The Jamo speakers at 150 Watts RMS per channel, will be deafening. I need to pass the signal through the computer for REW to make a configuration file of my "external" sound card, surely.

Thanks for your suggestions. They make me think through the problem, even when I disagree. I appreciate the time you have taken.

Wayne A. Pflughaupt said:

It’s the connection protocol that’s been used with REW from the very beginning. It does not produce feedback squeal, and does not bypass the computer. Please fully review this post from 2008, as well as the accompanying diagram.

See also the REW Help Files.

REW isn’t that difficult, really. People mainly run into problems when they don’t stick with the John’s recommendations for procedure and equipment.

Regards,
Wayne

Click to expand...

Hello Wayne,
You have directed me to a diagram that shows the setup for making measurements of the room acoustics. I already know how to do this. It is, as you say, not particularly difficult.
It was not clear to me how to calibrate the electronics, without measuring the room, and without using the microphone. I have third-party calibration files for the microphone already. I also do not want to have the speakers in this loop. Speakers are reactive, and will change their behaviour as I alter their positon in the room, and add acoustic elements to the room. I regard the speakers as part of the room to be improved.
I will try the loop from the output of the Schiit boxes to the microphone input on the Audient for this exercise. If that fails you will see me back here again. But I think this will work. I am waiting for the cable from Germany.
Thanks again for your help.

Wayne A. Pflughaupt said:

Probably should have clarified this early on, but:


What device is the digital optical output coming from?

Click to expand...

The Mac Pro tower computer has an optical fibre output. This goes to the Schiit DAC, which in turn is connected to the Schiit headphone preamplifier, which in turn is connected to the Yamaha amplifier, which in turn is connected to the Jamo speakers. This is the setup for normal use.

Wayne A. Pflughaupt said:

The point was to show that REW's recommended connection protocol is the same one you said wouldn't work, and instead give "feedback squeal".

Regards,
Wayne

Click to expand...

I thought you suggested that I connect the microphone through the Audient to the Yamaha Amplifier. This would bypass the computer and give a feedback scream.
The REW recommended connection for taking measurements is not the same as my setup, since they are talking about an external sound card, a digital device, which would ensure that the signals do not bypass the computer to which it is connected.

DanDan said:

The Rode NT1-A Microphone is not suitable for Acoustic Measurement. Sound Card Calibration or Loopback is not necessary. https://www.irishacoustics.com/forum/measurement-and-control/acoustic-measurement-primer

Click to expand...

You are right on both counts. However, for my home listening/recording room this microphone is good enough, and I have found a calibration file, attached. The irishacoustics.com reference you gave has this to say:
"The frequency response bumps of any reasonable mic are tiny compared to the 30dB anomalies we find in real rooms. Omni is necessary though because some of the acoustic action has direction. Jump in [...] and go for it with whatever mic you have at hand, even built in iMacs, Laptops, iPhones."
I may purchase a reference microphone, budget permitting.
The calibration of the electronics is not necessary, but since it seems to be not so difficult (at least, no longer so difficult as I now know what to do) I might as well. Besides, after going through the steps I will learn how to do it, and that is part of my aim with this project.

John Mulcahy said:

You may be misunderstanding Wayne's suggestion:

That means use the Audient mic input for the mic and use the Audient analog output to connect to the amp. You would need the Audient's "Monitor mix" knob turned all the way to DAW. REW would be configured to use the Audient for input and output.

Click to expand...

Hello John,
That is very helpful. Thank you. The Audient actually belongs to my son. I borrowed it for this project. I had no idea of how to use it correctly.
Thanks also to Wayne, whose good advice had fallen on deaf ears.

DanDan said:

"The frequency response bumps of any reasonable mic are tiny compared to the 30dB anomalies we find in real rooms. Omni is necessary though because some of the acoustic action has direction. Jump in [...] and go for it with whatever mic you have at hand, even built in iMacs, Laptops, iPhones."


The built in mics in mentioned ARE OMNI and often have quite decent Frequency Response.
A tight Cardioid Mic is not really suitable for Room Measurement, although it can get you up and practicing with REW.
The variations between Omni and Cardioid pickup are direction based and will very with the rooms. So I am not sure about the efficacy of that Mic Cal File. BUT why not try your new tool? Rotated the mic 90 degrees, and 180 degrees, taking measurements. See what happens to the Modes in the Waterfalls.....

Click to expand...

Hello Dan,
Thank you. That is a good suggestion. Perhaps I should get the right microphone from the start. I am working on a tight budget, and was hoping to get enough useful information without purchasing another microphone.