Vinyl Asylum

RE: Why are CDs digitized from master tapes?

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This Post Has Been Edited by the Author

In Reply to: RE: Why are CDs digitized from master tapes? posted by magiccarpetride on March 19, 2017 at 10:22:19

One of the most significant differences between CD (or FM, or streaming, or ...) and LP playback is the cartridge generates the AC signal used as the source of the performance directly.
Everything else uses a power supply which is then modulated to form the source of the performance. Thus, everything except a phono cartridge (or many types of microphone) is dependent on the power supply for it's sonic qualities, and there are not many people who would argue that power supply quality isn't relevant. Nor is it cheap, so it's often a target of compromises.
Regardless, the two represent fundamental differences in how the sound is created.
If you are cutting a CD master from magnetic tape (which is the old way, although some producers and engineers still use it today) alongside a concurrent master for vinyl, you have no choice but to experience the high 3rd Harmonic Distortion that is inherent in the magnetic tape format. So it's not a matter of lower distortion on the CD. 3HD will be in whole percentage points, rising from the low distortion floor at -20Vu.
Similarly, a recent audio meet on the west coast had a manufacturer of distortion analyzers present a demonstration on the audibility of various harmonic distortions. Members in the audience were asked to raise their hands when the musical performance sounded objectionable to them.
For the second and third harmonic distortion tests, some people didn't raise their hands before 2HD and 3HD reached as high as 30%. Whereas when the distortions were high order odd harmonics, such as 7HD, everyone had raised their hands before the levels reached 2%.
This fundamentally shows that the nature of the playback mechanism has significant effect on the realism of a recorded work. I don't find it surprising at all that some may prefer one or the other of CD, magnetic tape, vinyl through a cartridge, and so on. They all have unique characteristics that affect our enjoyment of the performance.
It should also be noted that CD, magnetic tape, and vinyl are all *storage media*. There is no reason why you could not record PCM data to a vinyl record, and use that as the source for playback of digital data. In fact this was done in the early days of computing.
Another method to playback vinyl uses lasers to read the analog data on the LP record. There is no physical connection to the disk itself, no magnetic cartridge to generate the AC signal. Those who have heard such a system often say it sounds more like digital than a cartridge-based playback of the same record.
I feel this supports the theory that there are fundamental differences in the way each technology replays the performance, and it should be noted that the laser method would be the same as CD in that there must be a power supply that is modulated, rather than the AC signal being directly created by the cartridge.
The source analog data is identical. There is no noise picked up by the laser due to dust particles. RIAA equalization is still required. In every respect it should be the ideal "phono pickup". Yet there are differences that cannot be easily dismissed.

Edits: 03/27/17 03/27/17 03/27/17 03/27/17 03/27/17 03/27/17 03/27/17 03/27/17 03/27/17

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