Additional factors to account for when calibrating?

[Ricci]

I know that you are supposed to use a cal file for your mic/spl meter to be used and also you are to create a cal file for your sound card. My question is if there are additional pieces in the signal chain why not make the cal file account for them as well? Like the Xenyx mixer, additional cables, and whatever else may be there?

Also has anyone tried to get the FR of their amplifier/ reciever/ EQ unit? I'd like to try to measure the overall response of my signal chain if possible. I'm not sure how I could go about it the best way though.

[salvasol]

Ricci wrote:

I know that you are supposed to use a cal file for your mic/spl meter to be used and also you are to create a cal file for your sound card. My question is if there are additional pieces in the signal chain why not make the cal file account for them as well? Like the Xenyx mixer, additional cables, and whatever else may be there?

Also has anyone tried to get the FR of their amplifier/ reciever/ EQ unit? I'd like to try to measure the overall response of my signal chain if possible. I'm not sure how I could go about it the best way though.

I remember that I saw a post on "How to check the crossover of the AVR" ... but I can't remember how ... I think Sonnie or Brucek posted that

[brucek]

My question is if there are additional pieces in the signal chain why not make the cal file account for them as well? Like the Xenyx mixer, additional cables, and whatever else may be there?

Yes, most members here that use a Xenyx mixer include it in the loopback when running the soundcard calibration routine, so that the soundcard cal file compensates for the mixers response.
That's all that's required. Cables? - they're already included in the soundcard file. What else is there?

brucek

[Ricci]

Well there's nothing else really. I was just checking whether everyone else is including the mixer, in their cal file.

[dguarnaccia]

Another question along these lines, how do you use both the Soundcard calibration file and the SPL meter calibration?

I see in the settings where it uses the Soundcard calibration .cal file based on the instruction, but I can't figure out where to include the .cal file for the SPL meter itself...

Anyone know?

Thanks,

Darren

[brucek]

Read the REW HELP FILES and the REW Connections and Cabling guide.

brucek

[dguarnaccia]

Hmmm...I followed all those instructions, and created the soundcard calibration file, which I used...

I just got confused when I saw additional .cal files for the RS SPL meter and didn't know where / when I was supposed to use those..I'm guessing I don't need it.

[salvasol]

dguarnaccia wrote:

... files for the RS SPL meter and didn't know where / when I was supposed to use those..I'm guessing I don't need it.

Yes you do!!!

If you don't upload those files, your measurement won't be accurate. Those files are used to adjust the frequency rsponse in the bass area ... for example, at 50Hz your SPL will read 63db; but with the files you'll get 68db ... that is because the SPL don't read exactly what it is

Hope this make sense

[Jerm357]

dguarnaccia wrote:

Hmmm...I followed all those instructions, and created the soundcard calibration file, which I used...

I just got confused when I saw additional .cal files for the RS SPL meter and didn't know where / when I was supposed to use those..I'm guessing I don't need it.

When your in REW click Settings,then right at the top on the left there will be a soundcard tab next to that is the Mic/meter tab, Click the Mic/meter tab and right under the Calibration section is where you want to upload the RS meter .cal file.

[brucek]

just got confused when I saw additional .cal files for the RS SPL meter and didn't know where / when I was supposed to use those

Reread this section from the REW HELP FILES.

brucek

[dguarnaccia]

gah! I'm a noob! I swear I've read that section 3 times and somehow I missed it every time...thanks for your patiences with us dense noobies

[DrWho]

Ricci wrote:

Well there's nothing else really. I was just checking whether everyone else is including the mixer, in their cal file.

I include it in my calibration simply out of principal, but if you measure your mixer or amplifier or wires or whatever, you'll find that any frequency response aberration they induce will be very predictable, but also extremely small compared to the behavior of the speaker.

One thing to note, which I see a lot of...when calibrating something like an SPL meter that starts rolling off at like 80Hz - your S/N ratio goes to real fast.

For example, assume that your electronics are perfectly flat and you have a mic that is rolling off at 12dB/octave starting at 80Hz. At 20Hz, you're 24dB down...so your calibration is offering 24dB of correction (in other words, your calibration is off by a factor of over 200). But it gets worse. Let's say your room has a 40dB noise floor and you leave yourself 10dB of digital headroom. You're now looking at a maximum dynamic range in your measurement of only 46dB. Now add in your 24dB of gain on the mic and now you're looking at 22dB of dynamic range at 20Hz. To give that some perspective...that's about equivalent to 5-Bit audio (yuck).

I know I'm making some assumptions and painting a worst case scenario here to make a point, but I bring it up to put into perspective some of the calibration files I've seen people post. How could one expect reliable 1dB accuracy from a tool that requires over 10dB of correction?

I figured I'd rant for a bit since the floor seemed to be opened up to calibration file issues

Btw, REW works real well for measuring anything that has an input and an output. You just gotta hook it up properly. You can even just plug your amp straight into your soundcard too....though if you go that route, it would be wise to install some protection circuitry just to make sure you don't over voltage your sound card...and make sure you make the protection circuitry properly....I blew up an amp by putting a diode in the wrong spot (oops).

[thewire]

People running electical appliances that use lots of power and might interfere with the measurement. During some testing I could not figure out why the buzzing noise was coming from my computer while measuring from the next room. It turned out my father was doing some cleanup with an electric leaf blower so I had to start over.

Then there is people. When I am in the room and measuring for every seat I try to spot myself in the measurement. This shows up as diffraction and I see it in measurements posted here very frequently. Ideally I am out of the room during testing and I almost done with the new equipment closet where my desk for measuring the room will be located.

[Ricci]

DrWho wrote:

Btw, REW works real well for measuring anything that has an input and an output. You just gotta hook it up properly. You can even just plug your amp straight into your soundcard too....though if you go that route, it would be wise to install some protection circuitry just to make sure you don't over voltage your sound card...and make sure you make the protection circuitry properly....I blew up an amp by putting a diode in the wrong spot (oops).

Thanks for the response Mike. I'm planning on measuring the low end response of my processor and reciever by looping back into the SC from the SW output. I'm going to measure my Rane PE17 too and try to check the center frequencies of the EQ bands. These always seem to be inaccurately labeled with analog devices. I'd really like to measure my Crown CE4000's FR but I'm afraid I will smoke my SC.