Soundcard calibration

[Conrad.]

Hi all,

I'd like to begin with a thank you; for providing some of the most knowledgeable and informative reading about sub equalization that I've read. Some of it I've even understood!

I’ve probably done things in the wrong order but I have a BFD and an analogue Radio Shack SPL meter on order to help me EQ a pair of Velodyne SPL1000s on the basis that EQing will improve things.

I’ve read through the stickies, guides and help files and I think I’ve got a rough idea about what to do when everything arrives (although no doubt I’ll be posting graphs and asking more questions/for help when they’re here) but I have an initial question about soundcard calibration.

My PC has an RME soundcard in it that sends a 5.1 signal to my receiver’s multi-channel inputs. These are then passed from the pre-outs to the power amp; apart from the sub, that goes direct from the receiver to the subs with a simple y-cable. I also have SPDIF from the sound card to the receiver so that I can use the receiver to process 2.0 signals into PLII. My PC also has onboard 7.1 audio which I could use.

My question is what output should I connect to what input for the loopback calibration? I’m pretty sure I want to use the RME over the onboard just because of the quality. I’m also pretty confident that I don’t want to use SPDIF out to SPDIF in (although would that work?). Also, as I’m only sub EQing should I just connect the sub out from the soundcard to the line in? I don’t even know if REW can see the RMEs individual channels so I might be consigned to using onboard.

I’m going to have to do a lot of playing around and testing but peoples initial thoughts would be nice to hear.

Apologies for the long first post and for falling quite so spectacularly at the first hurdle; thanks again!

Conrad

[Otto]

Hi Conrad, and welcome to the Shack!

Yeah, you will just go analog out of your sound card to the appropriate input on the receiver/preamp. Usually, we just use the stereo output of the soundcard, as it's the simplest method. If you go into a left or right input on your preamp (instead of a sub input), you will also be able to measure the response of the sub and mains together (though that will come after the sub calibration by itself). Also, I'm pretty sure REW is going to want to work with a stereo output (defaults to left), so it may not know how to handle a 5.1 output on your RME soundcard.

Since you'll probably have to go stereo out to the preamp, just do the loopback in the same fashion. Soundcard "line out" to soundcard "line in." Don't use "mic in." Do the soundcard cal, and go from there.

Good luck, you're on the right path.

[Conrad.]

Excellent, thanks for that. I've just had a quick check and I can choose which pair of channels I want to output the signal over. I guess for soundcard calibration I'll go for 1+2 - main L+R - with the input on the matched pair (I have 6 outputs with 2 inputs). When it comes to actually performing the sweeps I'll send everything out of the 3+4 channels - sub and center.

Now, I already have another question!

As I explained, I have a pair of subs (not co-located). Currently they're running from a single LFE output on my receiver; I also understand that the BFD supports two channels. In terms of connections, should I just run one channel into the BFD, split the output and EQ them as a single sub (they’ll always be on at the same time) or should I split the signal before the BFD and then EQ then separately?

Sometimes it’s nice to have so much flexibility but then sometimes an absolute would be a real relief!

[Otto]

Hi Conrad,

It's frequently recommended to EQ two subs at the same time. So, yeah, go to the BFD with the sub out of your preamp, and then split the output of the BFD. That way, you will EQ everything for the room as one. If you EQ one and then the other, such that each individual response is flat, it doesn't mean that it will necessarily be flat when you turn them both on. Of course, there's no harm in experimenting with using one channel of the BFD for each sub.