Signals from musical instruments in time domain - diyAudio
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Old 10th November 2007, 08:53 AM   #1
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Default Signals from musical instruments in time domain

For those who might be interested, I have prepared time-domain signal capture of horn and violin, from CD output. One can see limitations of the CD format. The sample rate of captures was 100 samples in one time div, i.e. from 500kS/s to 10MS/s.

Please read information about time/div at left bottom corner of the images.

http://web.telecom.cz/macura/minstruments.htm
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Old 10th November 2007, 10:56 AM   #2
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Very interesting, what is your conclusion. Would you agree that even CDs still has a long way to go before reaching a sound quality similar to analogue recordings?
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Old 10th November 2007, 11:06 AM   #3
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I agree completely. The only advantage of CD (vs. vinyl) is no "silent track" noise. I would also like to see 24bit/192kHz DVD-A and DSD SACD growth, but, unfortunately, commercial market dictates the trends.
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Old 10th November 2007, 12:46 PM   #4
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I can argue either side of the fence on this one. Well recorded CDs can sound great, probably as good or better than well recorded vinyl. They cannot, however, sound as good as a digital recording at a higher bit rate and depth. It wasn't clear what your original signal source was, but you can probably prove this with a decent condenser mic and interface on your PC. I haven't done that exact comparison, but the sound quality of recorded live instruments or vocals, and no processing, is beyond anything you ever hear on commercial CDs. I can also hear a difference when I transfer LPs to CD at 44.1 vs. 96 kHz. Small, but it's there.

Vinyl has it's own set of problems, but IMO these can be turned to our advantage as tuning tools. You can fool with cartridge type, stylus shape, VTA/SRA, energy absorption under the record (different types of mats), tonearm damping, and probably a dozen other variables. If everything is properly balanced, vinyl can sound darned good. The noise issue is minor on a good pressing, approaching inaudibility. Alas, the used records I buy are another story. A CD player, OTOH, only changes its character by a limited amount, regardless of the modification applied. Given the low source quality these days, I'm amazed that anyone spends more than a dollar ninety eight on a CD player.

Unfortunately, we can't record a high quality LP as we can do with a CD. If we could, and could do the kinds of signal comparisons we do for digital recordings, I think everyone would be pretty horrified at how badly LPs distort, and how adjacent groove modulation affects things, and how energy transmission through the vinyl causes ringing and artifacts. IMO, properly balanced, these things are what gives vinyl a certain sense of liveness and reality. IOW, the flaws improve the sound, as odd as that seems.

My take is that a better digital system would be great, but big changes would have to happen in the studio and subsequent processing, for it to make any useful difference. Right now, the source material is the limiting factor, not the bit rate or depth. I think they actually did a better job and targeted a more discriminating customer in the heyday of LPs.
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Old 10th November 2007, 01:00 PM   #5
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Quote:
Originally posted by Conrad Hoffman
IOW, the flaws improve the sound, as odd as that seems.
I think that the flaws (in a live recording) allow you to place yourself in the hall.

This is evident when they play the recorded live performances of the Met Opera.

Back in the early 1990's I visited Aureal Semiconductor -- they never made any money except when sound cards first came into vogue -- but the guys who ran the company were into electronic music and had gone the synthesis route in the time domain. They had analyzed brass and string instruments, the effects of a larger bell on a trumpet for instance, and had from this created virtual instruments which would have been physically difficult to implement in the real world.

Regrettably, the got crushed by Creative Labs -- Creative sued everyone including those who weren't infringing on their IP.
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Old 10th November 2007, 01:30 PM   #6
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For a comparison, a horn on vinyl:

http://web.telecom.cz/macura/vinyl_horn1.gif

http://web.telecom.cz/macura/vinyl_horn2.gif

Measured at 2.5MS/s sampling rate. Have a look at the rate of signal change, this is impossible to record on a CD.

(Miles Davis, Columbia)
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Old 10th November 2007, 04:26 PM   #7
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I see some stuff up at 16kHz. That doesn't seem so difficult. The two questions I have are, can you hear it, and what does it look like after being sampled at 44.1kHz, *at the analog output* of a decent CD player. I've been fooled looking at raw data that's scary, then seeing and hearing a tolerable signal on playback. I'd also add that I hear differences between the software drivers on different PC media players, and that's completely different compared to my CD player, so I'm not sure the HF behavior up where I can't hear it, is significant.
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Old 10th November 2007, 04:45 PM   #8
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It is much more than 16kHz. You can see edges shorter than 20us, followed by quite sharp change of slope. This indicate to frequency spectrum far above 20kHz. Reconstruction filter of the 16/44.1 would unify this by its impulse response. The resulting signal at CD output is convolution of samples with impulse response. Compare step response of the CD (same page) with horn2 sampled signal. Decent or not, 16/44.1 format always has sharp 22kHz digital brickwall in the chain.

Well, it is significant, as you can hear when you change linear PCM Fs to 96kS/s or 192kS/s.
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Old 10th November 2007, 04:56 PM   #9
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Few years ago I made a FFT analysis of that Miles Davis LP track. The result is here:

http://web.telecom.cz/macura/miles.jpg

As you can see, the frequencies between 20 and 30kHz are well seen, and there is a spectral content up to 40kHz. CD would sharply cut everything above 22kHz, and brings its typical technology, unnatural sound.
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Old 10th November 2007, 05:13 PM   #10
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I don't follow how you get from "the spectrum changes due to band-limiting" to "that's why the sound is bad."
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