Interesting Test

[DougMac]

I was going through some recent garage sale and Goodwill finds and pulled out an old Audio Fidelity test tecord. It has a series of test tones. The interesting thing is they recorded the high frequency tones without using the RIAA EQ, but they did use EQ on the low frequency (sub 1k) bands.

I recorded the test tones using DC6, then played them back while viewing the spectrum analyzer. I came up with some very interesting results. The liner notes stated that the high frequency bands were cut at a constant stylus velocity of 5cm/sec. When played back, the response was +-2db from 15k to 1k . The frequency bounced around a little. I attribute that to the record being pressed slightly off center (wow).

When I played the low frequency bands before RIAA EQ, the frequency rolled off 10 db. When I applied the paragraphic RIAA curve, it stayed within 2db down to 30HZ! I regard that as a good testimony to the accuracy of your present. Thanks!

I only wish they had included high frequency bands that were EQ'd so I could test that portion of the EQ.

BTW, I was testing a Grado Black using a Technics SP-15 turntable outfitted with an Audio Technica 1009 tonearm.

I have a Stanton 681 that I'll also test. I'd also be curious to run the signal through my NAD's intergrated amp's phono stage, at least the low frequency bands.

Doug

[Craig Maier]

Interesting. If you try that same test on Mentor, I know that its RIAA is within a very small fraction of a dB accurate across the entire curve. If you do not have that version and are interested, you can download a trial version and test it out. In other words, any errors obsereved would be from the test record, the phono cartridge or the flat preamplifier (which is ruler straight - flat if you are using our CTP family).

[NoProRalph]

Audio Fidelity Record.

I've got one of those test records I bought way back when. Audio Fidelity First Component Series. Have tried several times to make a "Test CD" out of it but without much luck. Unfortunatly I don't have a linear playback device.
but I recall they only certified a couple of turntable/cartridge combinations to track it back then. Somewhere in the early 60's I think.

NoProRalph

[Craig Maier]

Make Your Own Test CD's

Hi,

You can make your own Test CD's using your Diamond Cut Software's Make Waves Generator. There are two applications notes which will help which are AN1 and AN3. AN3 can be found at the following link:


http://www.diamondcut.com/Downloads/...DiamondCut.pdf


As a matter of fact, I wrote AN3 when I mastered the test CD's that we sell. AN3 is the exact signal set and procedure(s) that I used to create the test CD's that we sell - - - but you can make them almost for free if you have the time. Besides, it is kind of fun to do.

Craig

[NoProRalph]

Have already done that.

It was just an excersize and some fun. However how do you recreate the white noise stereo phase test?

Ralph

[Craig Maier]

What is a white noise stereo phase test? What is it supposed to do?

I would guess that it is just a two channel white noise test signal with a time delay between the two channels which can be accomplished via the use of the File Converter Filter's Time Offset Adjustment. Does that sound right?

[NoProRalph]

White noise phase test is:

On the record is a speaker phase test, where white noise eminates from outside of the speakers for a specific time then shifts to appear to come from a point betweeen the speakers. If the opposite occures the speakers are out of phase.
I don't see how that could be accomplished with a time delay. Maybe creating a white noise clip then reversing the phase of part of one channel with the "File Conversion Filter"? I haven't tried that.

Ralph

[Craig Maier]

Determining Proper Speaker Polarity or Phase

I have always found that a 100 Hz pair of sine waves does the trick, one on each channel. When the phase is incorrect, the acoustical signal is significantly less loud compared to when it is in phase. The file conversion filter can be used to invert one of the phases to see if this occurs. If inverting one channels phase makes the signal louder, then the speakers are connected incorrectly meaning that they are wired out of phase. Conversely, if inverting one channel's phase makes the signal softer, then the speakers are properly connected.

[NoProRalph]

Need something portable.

Will try to create something using your method, maybe try the white noise thing as well but I can't take DC6 and my computer when I'm setting up a system. I've got to come up with something portable.

Ralph

[Craig Maier]

Just make a CD ROM with those various signals that we discussed. The ROM and a portable CD player is all that you need thereafter. In other words, Track 1 is 100 Hz Stereo, both tracks in phase. Track 2 is 100 Hz Stereo, with the tracks out of phase as created by the File Converter Filter.

[NoProRalph]

Yeah. I recreated everything else on that record using the "Make Waves" some time ago. Then I just recorded a copy off the record for the phase check. This evening I've tried the other methods and while the white noise with part of one track inverted seems to work, for some reason the one off the record seems better defined.

Ralph

[DJBohn]

Hey NoProRalph, there have been a lot of test records over the years. I myself have a Soundcraftsmen Instructional Record that came with an Octave EQ purchase. On one side are mostly tones to match the EQ slides. On the other side of the LP was solid 1/3rd octave Pink Noise from beginning to end. But shouldn't one not trust used Test LP's? Don't the highs start getting wiped on the LP even after just a few plays?

[NoProRalph]

Until yesterday I would have agreed but according to Craig's test it appears not. He cites ? 2db response over the spectrum. And this is a record approximatly 40 years old. I suppose it depends mostly on how the record was maintained, how often it was used and the condition of the styli that has been used on it.
When I get some time I'm going to repeat his test on my record which I know has been used a couple hundred times, but has been carefully cleaned and stored after each use. Sometime after the holidays.

Ralph

[Dan McDonald]

And you're probably not going to get a lot of wear on a test record. At least not the kind of wear you'd get when people stacked up a pile of lps on a spindle and let them play for hours.

[DougMac]

Don't blame Craig

Until yesterday I would have agreed but according to Craig's test it appears not. He cites ? 2db response over the spectrum.
Ralph

I believe it's my test, not Craig's to which you refer. I don't want Craig blamed for my results!

I'd also like to clarify, if it's my test you're thinking about. The highest tone was 15k, so I don't regard that as covering the spectrum. Since it is a test record, perhaps it wasn't played enough to wipe out the higher frequencies.

I had the spectrum analyzer in fast mode. I'm going to play the file again and watch the freq and db readouts just for fun.

I wish there was more technical information provided for the recording technique. Did the engineers send the signal directly from the tone generator to the cutting head? (I suspect they did). How constant was the cutting lathe speed?

Much is made of the distinctive sound one cartridge family has compared to another (Shure/Audio Technica/Grado/Stanton/Benz). I thought the frequency curve characteristics (e.g. lower mid bump) would provide the coloration. I guess I was surprised at how flat the Grado is. I hope to get time to test the Stanton soon.

Doug