Check Levels, System Delay

[mstailey]

Hi John,
Thank you for sharing your knowledge with us by this program.

I did notice that in the measurement window when selecting Check Levels the SPL control shows 74-76db with a sweep level of -12 but the program comes back with a "Level to High" If I select check levels 2 or 3 times in a row (not changing anything on my AV unit, mic preamp or sweep level) it then comes back with Level OK.

After brucek's info on the system delay / speakers distance under the RTA post I tried this cool feature however it comes back to equal a distance of 18.08 feet. Actual distance from the front of the speaker to mic is 10ft 1 inch. Only 1 front speaker is being measured with all the other speakers and subwoofer disconnected in my example.

I'm sure in both cases it's something I'm doing wrong either by operation or setup?

[JohnM]

Hi Mike,

Check levels in the measurement panel warns if the input level exceeds -12dB FS, to make sure there is some headroom for the effects of room resonances. What level was the warning showing?

The delay measurement includes any delays within the processor, so if the processor is applying a delay (to account for another speaker that is further away) or if there is processing delay for the input you are using this will be added to the actual distance. What distance was reported for the other front speaker? It is also important to use a sufficiently wide sweep for that measurement, e.g. to 5kHz or more.

[brucek]

You can also verify that the System Delay function is being correctly reported by simply using a loopback cable on the soundcards right channel (from line-out to line-in) and do a full measure sweep.

It should return ~0.0 msec = 0.0 feet................

brucek

[mstailey]

Wow! The light bulb just turned on! Thanks brucek. After John's reply, re-reading your post on the RTA and reading over the highlights for version 4.10 it finally clicked.

JohnM was spot on. I'm using the loopback instead of the soundcard .cal file so I put the right channel sound card output into my right channel aux input. Now I've set the system for mono operation but noticed I've selected 7 speakers to play on the mono channel even though I had only 1 speaker physically hooked up. So, the delay was working (which all 7 channels are set at different lengths) coupled with the fact that I'm running the front 3 (L/C/R) thru a Rane THX44.

You can also verify that the System Delay function is being correctly reported by simply using a loopback cable on the soundcards right channel (from line-out to line-in) and do a full measure sweep.

It should return ~0.0 msec = 0.0 feet................

Now the lightbulb part - Based on the measurement you suggest (which I will do) and I get the expected results I should be able to add the Rane to the chain and that will give me the delay of the Rane, No?

I'll bet there is more fun to be had as the Rane should introduce a delay and I've not added that to the measurement(delay) distance in the A/V processor.

Man, when I grow up I want to be like brucek, JohnM and Wayne P.

[brucek]

I should be able to add the Rane to the chain and that will give me the delay of the Rane, No?

Well exactly.

Do your baseline check with a cable first and be sure you're at ~0.00msec. (The larger the bandwidth, the more accurate it will be, so sweep up to 20KHz).

Myself, I tested the BFD, (which we all claim adds a DSP delay of 0 msec or 1 foot), and indeed it measured exactly that. You can test all sorts of stuff. But, the interesting part is all your speakers. It's nice to be sure they are the same as tested with a tape measure.

brucek