calibration confusion! - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 37 Old 03-14-07, 05:21 PM
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Re: calibration confusion!

Quote:
Hope I have made a school boy error and it can be sorted simply.
The C-Media CMI8738 looks like a nice card. I do see where they supply just the drivers on their site. If all else fails you could uninstall the C-Media software package and then reboot windows, at which time it would "find new hardware" and would ask for the drivers if it needed them.

Either way, it sure looks like you have all the settings correct. I was hoping to see a mistake. You did say you loaded the software package from C-Media. This means in the Windows "Control Panel", there will be an icon to start that software package and play with its features. Look again that in addition to only enabling the card for two channel, that no wacky features are turned on. If that doesn't clear the problem, I would try the software uninstall and let windows handle it all on its own.

The last resort of course that can be used is to get the best soundcard calibrate file you can get and then edit it to remove the frequencies above where it starts to mis-behave. The file is a simple text file and can easily be editted with notepad and then resaved. Simply delete the entries above a certain frequency and point REW to the file as if it was fine. This works and simply doesn't provide compensation above that chosen frequency (i.e. 1000Hz)......I suggest this because in the frequencies of interest (i.e. 10Hz -200Hz), the file appears fine to do the job

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post #12 of 37 Old 03-14-07, 06:58 PM Thread Starter
 
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Re: calibration confusion!

Thanks Brucek,

I have tried many settings, but nothing shifts the issue.

So I have tried your suggestion of deleting everything above the 1000 mark. Then I ran a check with C weighting unchecked under mic/meter.

Can I work with this?



Hope so!

Graham
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post #13 of 37 Old 03-14-07, 09:20 PM
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Re: calibration confusion!

Yes, it will be fine for sub measurement.

If you set your graph axis to the standard of vertical = 45dB to 105dB and the horizontal = 15Hz to 200Hz that we use on the site for sub measurements, you'll see the loopback cable measures a flat line. So that means you have a response that eliminates the test equipment and all you'll be seeing in a room response will be your sound equipment. Be sure to load the microphone/meter calibration file for the meter you will be using when you take the measurements.

Be sure to set the target level to 75dB when measuring..


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post #14 of 37 Old 03-15-07, 01:01 PM
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Re: calibration confusion!

Graham,

Could you post images of the impulse response and the scope graphs when you do a loopback measurement? It might give a pointer to where things are going wrong.
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post #15 of 37 Old 03-15-07, 01:17 PM Thread Starter
 
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Re: calibration confusion!

Yes JohnM, I will certainly see if I can do that. Thank you.

Meanwhile... I have done my first graph! After so long without anything to show for it, I have managed to get a chart at least. Whether it is on the right lines is another matter. I get so confused about where I am supposed to alter the volume - mixer or amp. I have the amp quite high to get a level (about -12).

I find the relationship with room EQ (it's a denon amp) and auto setup, changing the subs input to set the highest level for the BFD, then altering the subs volume to match the fronts, then altering the volume in REL and I am totally confused.

I probably need to go back to basics and work through it again when I finally get the card sorted out - unless this chart is working?


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post #16 of 37 Old 03-15-07, 01:33 PM Thread Starter
 
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Re: calibration confusion!

Here are the charts as requested. Hope they reveal something.

Thanks for your interest.

Graham



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post #17 of 37 Old 03-15-07, 01:41 PM
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Re: calibration confusion!

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I get so confused about where I am supposed to alter the volume - mixer or amp. I have the amp quite high to get a level (about -12).
If that's the case, then raise the Wave and Output volume to 1.000 and then use the receivers volume control to set the Radio Shack SPL meter to 75dB.

Your chart is very good. (although you need the BFD for sure )

Quote:
I find the relationship with room EQ (it's a denon amp) and auto setup, changing the subs input to set the highest level for the BFD, then altering the subs volume to match the fronts, then altering the volume in REL and I am totally confused.
The input level to the BFD is totally contolled by the receivers volume control and trimmed somewhat by the receivers subwoofer speaker trim adjustment. We are simply trying to ensure the BFD gets an optimum a signal as possible. This means once the trim level is set for the subwoofer out of your receiver, then after that the volume level of the sub is best adjusted with the subwoofers own amplifier (as opposed to touching the trim again).

So, bypass the BFD (IN/OUT GREEN LED flashing and leave it that way for now) and setup your speaker levels with the receivers test tones (including the sub trim and subwoofer amps volume) as you normally would do.
Then put in a bass heavy movie and turn it up to the loudest you would ever use the system. If the BFD LED's are clipping in the RED, then turn the subwoofer trim down and turn up the sub amp to compensate. If the LEDs are not clipping, then turn up the trim to get the yellow LED on and turn down the sub amp to compensate.
There, now the sub trim is set for your system. Don't touch it again. The subs level will now be contolled by the sub amp volume.
You can put the BFD back on with the IN/OUT GREEN LED ON for filters engaged or OFF for filters disengaged. The flashing Green LED is filters off and the VU meters monitoring the input as opposed to the output level.

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post #18 of 37 Old 03-15-07, 04:06 PM
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Re: calibration confusion!

And when you get that sorted, I'd see if there is anywhere else you could move the sub to. Just a few inches can make a difference with troughs (42Hz 51Hz) which could be caused by unwanted reflections in your room interacting with your "original" sound. What are your room dimensions?
Bob

|JVC - PJ HD750 | Sony KL-50W2 |Denon 3805 + POA-T10 Biamp| Denon 2900 | B&Ws 604s3/602s3/LCR600s3 in 7.1 | SVS PB12-ISD | BFD | Sony PS3 Slim |SkyHD+ | Cables Scorpion & Mark Grant|
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post #19 of 37 Old 03-15-07, 05:49 PM Thread Starter
 
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Re: calibration confusion!

Hi Bob, giving me advice from both sides of the pond hey! Gord bless yer.

I have a longish room, 21 x 12.5ft x 10ft ceilings. It has a bay with large windows and blinds. It's rather echoey now the curtains are gone. There are a couple of beds in there as it's our bedroom at the moment. There is a side table over the sub to hide it. This is one of those marital compromises, so sticking it in the middle of the room is probably not going to fly.

I nearly set up my first set of filters, but despite setting up the BFD to accept midi control, it appears to send it via REW, but not a dicky bird from the BFD. Nothing at all flashes. That's when I leave it on channel 4. Maybe I am all too eager to blame the card, but I did try a couple of times. It was set up for the left channel, so it's not that.

Here's the room in case it helps anyone.



Graham

Last edited by blue_max; 03-15-07 at 06:05 PM. Reason: pic added
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post #20 of 37 Old 03-15-07, 07:35 PM
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Re: calibration confusion!

Quote:
I nearly set up my first set of filters, but despite setting up the BFD to accept midi control, it appears to send it via REW, but not a dicky bird from the BFD. Nothing at all flashes. That's when I leave it on channel 4. Maybe I am all too eager to blame the card, but I did try a couple of times. It was set up for the left channel, so it's not that.
Unless you have replaced the PROM in the BFD to upgrade to V1.4 firmware, then the Midi control doesn't work. You'll have to enter your filters by hand. READ THIS THREAD

Quote:
Here are the charts as requested. Hope they reveal something.
Not enough signal level. It's all down in the noise. Re-read my thread above about setting the levels.

EDIT: as an example here's an impulse response of one of my subs. I have noise around -50dB, but there is some good signal level, so it works out....

calibration confusion!-impulse.jpg

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