winopener, Interesting premise. IF however, you find harmonics of the subcarriers at 30 and 45 KHz something is wrong with the signal being sampled. The base 30KHz carrier unmodulated is a low distortion sine wave with 2nd and 3rd harmonic at least 60 dB down. Second harmonic would mean the carrier was becoming triangular and third harmonic would mean that the carrier was becoming square. If both occurred the carrier was becoming trapezoidal. The sampler, unless very nonlinear will not cause this problem.
Rumble tends to be a vertical movement which is Left-Right difference information and can be easily dealt with.
I have tested the ELP laser player and it is not as good as one would think. First the disc must be vacuumed before being played. Even then the 5 beam pickup is very susceptible to dirt impulse noise. The frequency response rolls of rapidly at 21 KHz.
Your Idea is interesting for archive purposes, but obviously not for real time playback.
Hi Lou,
- the sampling at half-speed is very non-linear; first of all, if done tapping the signal out a phono preamp, RIAA will be wrong big time, so
1. the signal from the phono cartridge is going thru a flat pre-amplifier
2. after the sampling the resulting file is doubled in frequency
3. then RIAA is applied in software.
The harmonics i have seen are between 2. and 3., applying a RIAA curve get rid of most of them.
Any idea to deal with rumble is very welcomed, and not only by me.
ELP may be susceptible to dirt anyway but i think it still holds the advantage of a better separation between channels, which is *the* critical element for any matrix decoder. I know Toshiba did a optical LP player in the seventies, do you had any experience on this?
I prefer to avoid the "magic"
of real time playback of quad sources for various reasons:
- wear: if something happen to the very rare japanese cd4-only copy of a very sought-after LP, chances to find out another one are pretty slim;
- sound can be improved: NR, decliking and other digital approach can improve a lot the sound just leaving the sound alone and getting rid of the noise due to the media used; especially true for quad carts.
- ease of use: playing a cd4 records on a car is kinda hard... unless it is converted in another format; digital multichannel players, be DD, DTS or DVD-A are available and easier to find than Q8, plus they performs a bit better
than carts.
- a digital archive can be stored in the little space of a hard disk drive, which make "portability" something easier than before (when you had to move every 3-4 year you start to appreciate that!) and is a near-zero cost sources of a new fresh digital multichannel disc if the first one goes bad.
So, archiving of the analog sources IS my goal for these quad sources, then enjoyable in digital format without any hassle of something going wrong.