Setup/measurements on a mac + interface (initial questions)

[donalddemon]

I didn't want to further hijack the other thread I posted in so I just had a few general questions on the setup here, this is my first time using this software. I am testing my "control room" in my basement studio, which is a typical problematic small room dimensions; 13.5' long x 11' wide x 7' ceiling height. I have some broadband absorbers on the back wall and bass traps behind the monitors. I'm using a Focusrite Clarett 8pre interface into my 2018 iMac running High Sierra 10.13.6 and REW 5.20 beta, into Pro Tools 2019. My monitors are Neumann KH120's with no sub. I'm using 2 Behringer ECM8000's a friend gave me to test with.

I don't have an SPL meter and only used a phone app SPL, which I'm sure is not accurate at all. In fact, I just bypassed the SPL cal altogether. Should I look into getting one, does it make a big difference on accuracy?

I downloaded the ECM8000 cal file, though I understand they should be unique to each mic, I figure it's better that nothing. I was trying to calibrate the soundcard (interface?) and hooking up a connection from a line out to line in was giving me abnormally low input levels. Somehow, I came up with the configuration in the attached pic and it worked, though I have no clue how it's doing it or if that is right. My ECM8000 is on input 7 of my interface and I had input 6 as the in/out so I guess it was using the mic as the input rather than the interface output? It may have something to do with me doing something wrong in the Focusrite Control monitoring software, which has been confusing for me.

I was able to take a few measurements but only through the sweep and not the pink noise, still haven't figured out how to get that working yet. I don't know how accurate these are given that I am missing several seemingly important steps. Am I on the right track or is my setup wrong?

 

[John Mulcahy]

The SPL doesn't really matter, just use a comfortable level. Measurements look slightly unusual, don't usually see such sharp peaks. Probably worth attaching the mdat file.

 

[donalddemon]

The SPL doesn't really matter, just use a comfortable level. Measurements look slightly unusual, don't usually see such sharp peaks. Probably worth attaching the mdat file.

Hi John, thanks for checking this out for me. I have probably not done something right along the way. Attached is the mdat file. I think that includes everything I did yesterday.

 

[John Mulcahy]

Measurements look OK, though I wonder what sample rate the interface is set to in Audio Midi Setup, does it match the 48 kHz rate selected in REW? There is a feature before the IR peak that often indicates a sample rate mismatch, but it might be due to some DSP activity. Worth measuring L and R separately. The peaks at 245 Hz and 465 Hz really are severe.

 

[donalddemon]

Measurements look OK, though I wonder what sample rate the interface is set to in Audio Midi Setup, does it match the 48 kHz rate selected in REW? There is a feature before the IR peak that often indicates a sample rate mismatch, but it might be due to some DSP activity. Worth measuring L and R separately. The peaks at 245 Hz and 465 Hz really are severe.

The interface is setup as 48k in my Control monitoring software. I do my sessions in 48k as well. I will try L & R separately next time. My guess is those spikes are from the less than ideal input levels I had. I really had to crank up my mic input on the interface to get around -18 db and it felt like my ECM8000 was on the verge on feedback. Something seemed off with the input levels, like I shouldn't have had to push the input so far. Maybe those spikes are from the onset of feedback?

 

[John Mulcahy]

Monitoring must be completely off for valid measurements, none of the input can be routed to the output.

Check the Audio Midi Setup config, that determines what will be available for REW.

 

[donalddemon]

Monitoring must be completely off for valid measurements, none of the input can be routed to the output.

Check the Audio Midi Setup config, that determines what will be available for REW.

Sorry if I misunderstand, do you mean the monitoring software should be off?

I took some some screen grabs of my Audio Midi Setup since I don't really know what I'm looking at.

 

[John Mulcahy]

Sorry if I misunderstand, do you mean the monitoring software should be off?

I mean that if you tap on the mic or speak into it none of that signal should be routed back to the outputs you are using for measuring.

Audio Midi Setup looks OK.

 

[donalddemon]

I mean that if you tap on the mic or speak into it none of that signal should be routed back to the outputs you are using for measuring.

Audio Midi Setup looks OK.

Got it, that may have been the problem with the spikes then. I'll have to try again with a different routing setup. I guess I'll need to dive deeper into the monitoring program, it's not very intuitive. Thanks!

 

[donalddemon]

I mean that if you tap on the mic or speak into it none of that signal should be routed back to the outputs you are using for measuring.

Audio Midi Setup looks OK.

Ok, solved it I think. I muted the output of the mic channel. Do you think this look more like useful measurements?If so, I guess I should go ahead and take several more from different positions at my listening area?

 

[John Mulcahy]

Looks much better

 

[donalddemon]

Looks much better

Cool! You were right, monitoring was the problem, I knew I wasn't supposed to be hearing the mic feedback like that. Ok, now to learn what this all means! Thanks