Capturing RTA peak data as measurement

Roger Dressler · Oct 23, 2017

Am new around here, but have been a fan of REW for years for room measurements and EQ tuning -- all the way back to my Tag McLaren processor days.

Am now trying to compare two audio clips -- same song, one from CD, the other from LP. To me, they sound different in the high frequencies, so I thought about taking an RTA of each for comparison.

The RTA tool has a peak display feature that looks ideal. It is the red trace in the plot. It shows the peak levels over the entire duration of the audio clip. The black trace is the instantaneous spectrum of the audio at the moment the RTA was stopped. I'm not interested in that for this purpose.

When I Save the RTA to store the measurement, it transfers the black trace data, but does not capture the red peak data. Is there a way to do that?

Thanks!

Matthew J Poes · Oct 23, 2017

I would think a more precise and possibly easier way to do this would be to record the output of the CD player and record player and then analyze the frequency spectrum of the two files.

Otherwise I am not aware of a way to do what your trying to do.

John Mulcahy · Oct 24, 2017

The latest beta allows audio files to be imported and their frequency responses or spectrograms directly compared. For 44.1k sample rate the import will accept the first 89 seconds of data.

Roger Dressler · Oct 24, 2017

Superb! I knew I'd get the answer here. Thanks John.

John Mulcahy · Oct 24, 2017

There's a bit more about it in this thread.

Roger Dressler · Oct 24, 2017

That worked great! I loaded the CD and LP captures (20 sec each) and applied 1/3-oct smoothing. It showed an increase in HF above 5 kHz, reaching 3.3 dB at 10 kHz from the LP (red) version vs. the CD (blue). Just as I was hearing.

Matthew J Poes · Oct 24, 2017

That’s a neat and interesting finding. I wonder if that could be attributed to the record mastering or to the r cord playback Chain. Certainly needles and RIAA curves can have differences like that too.

Roger Dressler · Oct 24, 2017

That's a good question. The particular recording in this case is from Sheffield Sound Labs, Ghost in the House, direct to disc vs their tape-to-CD version. I think they did very little, if any, of the usual processing that occurs during mastering -- which is what piqued my interest in why they did not sound identical. Was the LP revealing more detail that the lowly CD format could not convey, or was this a side-effect of something more fundamental, like a response difference?

I have a few other recordings for which I was provided both the CD and LP versions, and all regardless of origin they share the same audible elevation in brightness (aka "detail"). Based on that it seems to be something about the LP playback chain afoot here, be it the preamp EQ or cartridge characteristic/resonance.

Maybe I'll put those other recordings thru the same analysis just to see if there's any consistency.

Matthew J Poes · Oct 24, 2017

Roger Dressler said:
That's a good question. The particular recording in this case is from Sheffield Sound Labs, Ghost in the House, direct to disc vs their tape-to-CD version. I think they did very little, if any, of the usual processing that occurs during mastering -- which is what piqued my interest in why they did not sound identical. Was the LP revealing more detail that the lowly CD format could not convey, or was this a side-effect of something more fundamental, like a response difference?

I have a few other recordings for which I was provided both the CD and LP versions, and all regardless of origin they share the same audible elevation in brightness (aka "detail"). Based on that it seems to be something about the LP playback chain afoot here, be it the preamp EQ or cartridge characteristic/resonance.

Maybe I'll put those other recordings thru the same analysis just to see if there's any consistency.

It’s a cool find to be sure. My own record playback chain suffers the opposite issue. The needle I use has a somewhat rolled off top end and I redesigned the riaa stage of my preamp to be as perfect as I could. The net effect is that my records have a more warm presence that seems sometimes lacking in detail. To many the untrained ear a back to back comparison makes the cd sound better. In my opinion they sound different. You have to get used to each before judging due to the tonal difference. I mostly like the records because many of them are better mastered, less compression. Sheffield tends to be an exception to this so I imagine that careful listening would present something similar, just a different sound.

Capturing RTA peak data as measurement

Roger Dressler

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