Another connection question - M-audio 410 & SPDIF

[maneuen]

I've seen the diagram regarding connecting "R" output to processor and "R" input to RS meter. I have a m-audio 410 sound card, so I have an rca input, but I am using the spdif out connection for all the sound from the htpc. ie. everthing is sent to the processor via my single spdif connection and the processor is doing all the channel seperation.

Will REW work this way? ie. digital out to receiver and analog in from RS meter. If not, wouldn't changing to analog out on the htpc in order to do the measurment distort my results, since when it actually came down to watching a movie or listening to anything, I would only be using the digital out.

[brucek]

Will REW work this way? ie. digital out to receiver and analog in from RS meter

Yes, but the results won't be as accurate since you won't be able to compensate for inadequacies in your soundcards frequency response because you won't be able to carry out the loopback test to create the calibration file for the soundcard. It will still work without this file, but it won't be as accurate.

wouldn't changing to analog out on the htpc in order to do the measurment distort my results, since when it actually came down to watching a movie or listening to anything, I would only be using the digital out.

You may be a bit confused here. The purpose of using REW is to create an accurate frequency response for your room and speakers, specifically to create a set of equalizer filters for a BFD to produce a smooth subwoofer response. Doesn't really matter what source you use for movies etc after the subwoofer response has been equalized. REW and your PC are only being used as a tool.

brucek

[Vader]

you won't be able to carry out the loopback test to create the calibration file for the soundcard

Bruce, you just had to go and spoil my parade, didn't ya Seriously, I was thinking that the only kind of connection where each speaker could be measured seperately (other than 5.1/7.1 analog inputs or physically disconnecting speakers not being tested) would be a digital connection. What other options would we have (the help file in REW says that the optimal connection would be one which allows for each speaker to be isolated). As maneuen said, letting the AVR do the signal routing would seem to be ideal. Is there a sound card that has optical input/outputs? What about sound meters?

[brucek]

letting the AVR do the signal routing would seem to be ideal.

Well, I guess you have to determine what the purpose of the exercise is. If we want to equalize a subwoofer in a room and then perhaps tweak it by adding in a set of mains, there's no need for more than a simple analog signal to the processor. I see little reason in using the steering of a processor in that regard.

brucek

[Vader]

I guess I was referring to the following from the REW help files under 'Getting Started --> System Connections'...

If connecting to an AV processor input, the input used should ideally be one that the processor can route to any speaker output.

f the processor does not have such a signal routing facility it may have 5.1 or 7.1 analog inputs that can be used, but in some cases bass management will not be applied to such inputs, limiting the ability to check sub/main speaker integration.

So the only way to test the response of each individual speaker is either to use the 5.1/7.1 anlog inputs, or route the signal through all speakers and physically disconnect the ones not being tested? Please understand, I am not trying to be difficult. There is so much I don't understand yet...

[brucek]

So the only way to test the response of each individual speaker is either to use the 5.1/7.1 anlog inputs, or route the signal through all speakers and physically disconnect the ones not being tested?

I guess there might be an occasion where you want to observe the crossover region of the center and rear speakers. In that case the 5.1 bypass input wouldn't do much for you. I don't know of any processors that would steer to a specific speaker without the other speakers playing too, so you would indeed have to physically disconnect them.

If you were attempting to test each speaker on its own with crossover and in its native position, then you would just have to connect each one individually as a left or right main and run the sweep.

Is this something you're trying to attempt?

brucek

[maneuen]

Thanks for the replys, it sounds like I should just use a the creative usb soundcard and my laptop rather than the htpc and m-audio.

My thinking for wanting to use the htpc was to preserve the same audio chain that I actually use. I understand that I am tuning the sub to the room, but I'm not sure how much variance there is between sound card output / type of output levels and rca input vs. digital input on the receiver.

suppose with the m-audio digital output I have to turn the receiver up to x in order to achieve 75 decimals. But with the creative usb sound card and rca output/input I must turn the receiver up to "x-10" to achieve the same output level. Then in reality I have tuned everything to a level that is too quiet for actual use. Do you see my reasoning, or am I overlooking something?

[Vader]

Is this something you're trying to attempt?

Not now, as I have no means to equalize it anyway (I am waiting to upgrade to uncompressed Dolby/DTS, and then use the onboard room EQ). I thought EQ'ing all speakers seperately was standard, but I guess I was chasing another wild goose. This is not a learning curve - it is a learning cliff (but I'm having fun all the same). Thanks for your answers!

[brucek]

Do you see my reasoning, or am I overlooking something?

What you're overlooking is that no matter what the soundcard you use, it's response inadequacies are compensated with a calibration file, and its output/input level anomolies are compensated for during the REW setup where all the levels are set to a level of (for example) 80dB. The entire purpose of the exercise is to get filters set in a BFD or to modify room layouts/ equipment placement for the best response.

Once the equalization filters are set on the BFD, then it is of no matter what level you play back through your system.

brucek