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Computer program to establish CD source as vinyl or tape?
muse2u
post Dec 23 2012, 19:01
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On several occasions I have purchased compilation CDs of 60's artists, where it was not clearly indicated what the analog source of the CD was. The artists made a brief appearance on the scene, recorded several vinyl singles, no albums and subsequently disappeared. From a listening test, the 'feel' of the cCD is that of a mint vinyl source with painstaking restoration. In all likelihood the original master/session tapes were not available and mint vinyl copies were the only alternative to creating the comp. Listening for telltale pops and clicks does not reveal the source in this case. Sometimes there is a little distortion in high volume/high frequency audio where the needle/cartridge did not track properly.

I assume that a vinyl sourced CD must have some measurable characteristics, other than pops and clicks, that are different from a tape sourced CD. Is anyone aware of a program that will analyze a CD (direct or after transfer to hard drive) for these differences?
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slks
post Dec 24 2012, 00:14
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In general vinyl rips will have an altered frequency response than the original tapes. However, the exact variations will depend on the equipment that was used to rip the vinyl.

Vinyl rips also have low-frequency rumble noise from the turntable, but again the degree and character of that noise will be different on different equipment, and it'd be difficult to distinguish that noise from tape/studio noise that's in the recordings anyway.

Add in the fact that these rips have almost surely gone through some post-processing - nose reduction, pop removal, additional EQ - there's just too many variables to make that determination with reliability, especially not in an automated way.


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cliveb
post Dec 24 2012, 09:03
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As slks says, there are plenty of post-transfer processes that could be used to eliminate pretty much all of the tell-tale signs that the source was vinyl. Easiest of those to accomplish would be various types of EQ to remove rumble and adjust the frequency balance, plus broadband noise reduction to reduce the characteristic vinyl surface noise "hash".

As for removing all the pops and ticks: while it can be done with enough effort, the cost of doing it well for a commercial release is sufficiently high that it wouldn't get done for a release where sales volumes are likely to be low. It will either be skipped altogether (in which case careful analysis would reveal some minor vinyl ticks), or it would be done quickly with an automated tool that would leave behind the typical artefacts of automated click removal: low level "thuds" and "plops".

I reckon I could fairly quickly establish whether a commercial CD was sourced from vinyl. A needledrop created by an enthusiast willing to put in the effort is another matter. If you want to try, and there really are no clicks and ticks, then I recommend you look for those "thuds" and "plops".
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Arnold B. Kruege...
post Dec 24 2012, 23:46
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QUOTE (slks @ Dec 23 2012, 18:14) *
In general vinyl rips will have an altered frequency response than the original tapes. However, the exact variations will depend on the equipment that was used to rip the vinyl.

Vinyl rips also have low-frequency rumble noise from the turntable, but again the degree and character of that noise will be different on different equipment, and it'd be difficult to distinguish that noise from tape/studio noise that's in the recordings anyway.

Add in the fact that these rips have almost surely gone through some post-processing - nose reduction, pop removal, additional EQ - there's just too many variables to make that determination with reliability, especially not in an automated way.


Anything that has been put on a LP and then played back will be FM-modulated in some characteristic ways. However, measuring these without a clean reference recording of the same basic recording can be difficult.

External steady tones such as the power line, monitor sweep signals, switchmode power supplies, and analog tape recording bias signals may have leaked into the recording and can then be used to detect these kinds of FM distortion.
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muse2u
post Dec 28 2012, 18:20
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Thank you all for the replies.
I have some experience with digital audio restoration techniques using DART computer programs to compensate for peculiarities on my vinyl records, so I have some understanding of what you are writing. I was hoping that a simple frequency analysis program would establish the source, but it sounds like it is more complicated than that. I don't have access to any specialized hardware so I will have to rely on my ears and listen for clues. What I might do is e-mail the cd label and ask them to clarify.
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mzil
post Dec 28 2012, 18:50
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QUOTE (muse2u @ Dec 28 2012, 13:20) *
Thank you all for the replies.
I have some experience with digital audio restoration techniques using DART computer programs to compensate for peculiarities on my vinyl records, so I have some understanding of what you are writing. I was hoping that a simple frequency analysis program would establish the source, but it sounds like it is more complicated than that. I don't have access to any specialized hardware so I will have to rely on my ears and listen for clues. What I might do is e-mail the cd label and ask them to clarify.

I wouldn't listen to the music, I would look at it.

Like Arny wrote, open a real-time spectral analysis image of the music and look for signature spikes at, for example, 50/60 Hz (EU and US AC hum) or ~15 kHz for CRT TV scan frequency noise. Magnify the view and if you see the spike wavering up and down in frequency every 1.8 seconds, then you know for certain the music is being generated by something which rotates at 33.33 rpm (but there is some wow due to an off center spindle hole, record warp, etc causing the frequency wavering).

This post has been edited by mzil: Dec 28 2012, 18:51
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