Rives Audio Test CD

[breadman]

I obtained of the Rives Audio Test CD 2 and a Radio Shack analog SPM to check out the audio frequency response of my 6.1 system. I used tracks 32 – 62 as recommended by the manual to compensate for the non-linear response of the meter. Everything went much as expected, fairly linear response only bouncing a few DB’s here and there, until I reached the higher frequency. I see a 15db decrease between 6300hz and 8000hz. Then another 10db decrease between 10000hz and 12500hz. I was rather disappointed with the readings and saw the same results in stereo mode or 6 channel stereo playing all speakers. I played the tests on another stereo system in another part of my house with similar results.
These results are not what I expected. I am at a bit of a loss as to the serious roll off. I find it difficult to believe that both systems have similar problems and assume that it must be the disk or something in my setup. Any advice? Does anyone have any experience using this CD?

 

[gene]

Welcome to the loudspeaker/room interface, the most critical component in your system. It is not atypical to see a 20db roll off at 20kHz when at the listening position off axis to the main speakers. You may wish to recheck by placing the mic a meter or 2 away from the acoustic center of a main speaker and see what it does. Be careful not to overdrive the mic. I would set it to about 80dB 1 meter away.

 

[plhart]

Understand that the mic in the RS meter probably costs the manufacturer $0.50! This is a very inexpensive piece of test gear which means that unit-to-unit variation in mic elements is probably huge and completely acceptable to RS. Also understand that flat high frequency response is much harder to achieve at the high end of the frequency spectrum, especially with such a large diaphragm microphone. Typically an instrument grade mic will be 1/4" to 1/2" diameter and cost $2000 or more.

The RS meter also has a fixed C-weighted frequency roll-off for the low end of the scale which can't be defeated. The Rives test disc attempts makes up for the C-weighted roll-off at the low end to give a simulation of a flat response reading were there no built-in weighting factor applied.

 

[breadman]

Thanks for the input. Actually, I originally just wanted to use this test setup to get a rough idea of how my subwoofer integrated with the main speakers. From what I found setting the crossover lower (around 50hz) seems to measure and sound the best. I just looked at the full spectrum as an afterthought and needed to be reminded of the equipment limitations.

 

[dr.sound]

PLHART,
I beg to disagree about the Radio Shack meter. It is a standard reference meter for calibrating SPL on "the Dub Stage". It is accurate for checking pink noise for speaker calibration. I do agree that it is NOT to be used for frequency room EQ broadband calibration. You need an RTA with a calibrated Mic.
My room www.thedubstage.com
has been calibrated by Dolby Labs for the standard "X curve" which is flat to aprox. 2K then proceeds down 3db per octave. There is also a modified "X curve" for smaller rooms (which are what nearly all your readers have) which is flat to 2K then down 1.5 per octave. Some take it flat to 4k then do 3db per octave.This is probaby a better set up for most people.
Here is another link that your readers may find interesting. It is about "Room Calibration for Film and TV Mixing". It has some very interesting reading if your readers want to understand better what the Pro's do for standard calibration. The link is:
http://duc.digidesign.com/showflat.php?Cat=&Board=UBB6&Number=529464&page=0&view=collapsed&sb=5&o=31&fpart=1

A very common mistake by Audiophiles is to have a very flat frequency response using uncalibrated Mics and test equipment thinking that is what it should sound like.
It’s only after mixing in a calibrated “dub stage’ does one know what the original mix should sound like. Unfortunately many if not most of the “Home Theater” manufactures don’t have a clue what a “Theater” should sound like!
Thank you for letting me educate your Forum readers in hope they can enjoy great sounding “Home Theater” the way we do when we work or should I say play while we mix!
Marti D. Humphrey C.A.S.
Re-Recording Mixer
www.thedubstage.com