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Hi all,

I did a search for this topic here on the forum, but didn't find anything. My apologies if there is something out there...please feel free to direct me to a thread if there is one.

I've attempted a few measurement captures myself using REW, while playing frequency sweeps with a test LP, but I'm not convinced the results are accurate...or else I don't understand how the software is processing results. One part that confuses me is how the software (after clicking 'Start Measuring') performs its sweep in just a few seconds (and I see some type of result), but then the sweep on the test LP lasts much longer, so are they working together somehow? I discovered how to perform smoothing on the graph (1/6 seems to work well), but again, I'm not confident in the raw data.

As far as interface, I going from my phono preamp output into a passive A/D converter (xitel Inport Deluxe), which has a USB output, and then into my PC's USB input. The 'soundcard' is an integrated Realtek on the motherboard. Obviously, this is not 'laboratory-grade' equipment :geek: (not to mention, "old"), so I'm not expecting laboratory results. But, I'm hoping to, at least, have some level of confidence that the results are usable,and consistent. I want to capture FR graphs for the same cartridge, but utilizing different load settings in the phonostage, so even if not 100% accurate in some respects, having consistent results is important, directionally. I hope that makes sense.

I'm guessing that calibration and setting appropriate dB levels will be critical, so any advice is much appreciated! TIA
 

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You do not measure cartridge response with REW. What you measure with REW is in the NAME of REW... ROOM EQ Wizard. You measure your ROOM. And your ROOM with overwhelm anything your turntable does during the ROOM measurements. To measure the output of a phono cartridge, you connect an oscilloscope to the output of the cartridge (low level output) or to the output of a phono stage that includes RIAA EQ necessary to reproduce LPs so they sound right. The cartridge measurements will be ELECTRICAL measurements, not ROOM measurements.
 

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You do not measure cartridge response with REW. What you measure with REW is in the NAME of REW... ROOM EQ Wizard. You measure your ROOM. And your ROOM with overwhelm anything your turntable does during the ROOM measurements. To measure the output of a phono cartridge, you connect an oscilloscope to the output of the cartridge (low level output) or to the output of a phono stage that includes RIAA EQ necessary to reproduce LPs so they sound right. The cartridge measurements will be ELECTRICAL measurements, not ROOM measurements.
Sorry you haven't been keeping up, Da Wiz. REW has been adding capabilities quite regularly since it was introduced. With the right interface it is now a powerful piece of bench test equipment, and widely used that way.

But back to the point...measuring cartridge response is tricky in general, for a couple of reasons. First, you are limited to test signals created by others--you can't feed a test signal from REW into the cartridge in most cases. You are stuck playing back test records. There are lots of different test records, and the ones that are made to test frequency response don't all agree with each other that closely. And the signals on the test record may or may not be formatted in a way that fits what REW is looking for. Another complication is noise pollution. The signal coming back from the TT/Cartridge/Phono stage will have a variety of noise signals mixed in. Probably the most troublesome one will be the random impulse noise. Most test equipment just doesn't know what to make of that.

In order to get a decent measurement of a frequency sweep, REW would have to be looking for the same length sweep as the one on your test record. And you would need to be able to synchronize the software to the start of the sweep somehow. Historically this has been done: there were test records with tones before the sweep which would trigger a chart recorder, or the operator could be asked to count so many seconds from the end of the cue tone & then start the chart recorder. This may sound primitive, but they were attempts to solve the sync challenge with the tech that was available then. The tech has changed but the challenge is the same. Time the sweep on your test record. Look for a setting in REW that lets you change the time of the sweep it's expecting. Figure out some way to tell when the sweep is about to start, and practice cueing REW till you can get it pretty close. Doesn't sound easy, does it? It isn't.
 
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