| Title: | Welcome to the CD Notes Conference |
| Notice: | Welcome to COOKIE |
| Moderator: | COOKIE::ROLLOW |
| Created: | Mon Feb 17 1986 |
| Last Modified: | Fri Mar 03 1989 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 1517 |
| Total number of notes: | 13349 |
I believe that the CD recording process does require any equalization
due to the inherent process of D/A conversion. Equilization is
usually employed when the media used has some limitation that must be
compensated for. In phono records this process includes reducing the
amplitude of low frequencies and boosting the amplitude of high
frequencies. I a 60 Hz signal was recorded in an unequilized state
^f
the physical space required on an LP would be drastically reduced. As
a matter of fact the advent of the term LP came about by employing a
different equalization curve that allow more music to be recorded in
the given space thus coining the term LP for Long Play.
Tape recorders use the equilization principle to achieve the frequency
response necessary for high fidelity by boosting high frequencies when
recorded onto the tape.(Actaully a lot more is involved but I'm not
able to recall the exact details.) Biasing is a method of achieving
higher frequency response by using a high frequency(well above 20KHz)
signal to add energy to a lower frequency(15-20Khz) which allows a higher
amplitude to be recorded onto the tape. Since this is only done in the
recording process the Bias signal is not required during playback.
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I just noticed that the first line of this note is in error. It should
state that equilization is NOT necessary for recording a CD. Everything
that follows is correct(at least gramatically, I think).
The Biasing subject brings to mind a "hipe" that was used when automotive
tapedecks advertise that they are Metal Capable. To play a metal tape
the only thing that is necessary to achieve correct response is Equilization
This equilization is the same for both C02,C02 Equivalent, and Metal tapes.
Even if this equilization feature is not present, the tape still sounds
respectible. The only time special electronics and heads are necessary is
to record on a metal tape.
--Dale
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 105.1 | AMOS::REUTER | Mon Apr 08 1985 00:48 | 28 | ||
.0 is incorrect on several points: First, tape bias is not used to "add energy" to any of the frequencies being recorded on a tape. It is used to make the recording process reasonably linear. If the audio signal was sent directly to the head, magnetic hysteresis (e.g. once the head is magnetized it wants to stay that way) would cause terrible nonlinearity. The bias signal corrects that problem, but does affect frequency response depending on the magnetic characteristics of the head and the tape used. This is why tape deck spec's are usually given for one or two specific brands of tape. A real tinkerer would adjust his deck for the tape being used. Pro equipment puts the bias and equalization controls somewhere where a technician can fiddle for a specific brand of tape. Second, there *should* be a difference between "metal capable" and older auto cassette decks--harder heads. The metal tapes are more abrasive than oxide tapes, so harder heads are needed to prevent excessive wear. The million dollar question here is whether or not that "metal capable" label really means this! The other comments about record and tape equalization look accurate. To the best of my knowledge, CDs have no equalization other than the high-frequency cutoff needed to get rid of the sampling artifacts. Jim | |||||
| 105.2 | JAKE::ROBERTSON | Mon Apr 08 1985 09:35 | 16 | ||
I believe that the binder used on metal tapes is the same as on oxide tapes. The story of metal tapes wearing out heads is the same one used on true Chromium Dioxide tapes. The actual particles never touch the heads(or they shouldn't). There is no proof that one type of tape wears out heads any faster than another type. One doesn't have to buy a professional tape machine to set bias levels. My Nakamichi has these features right on the front panel. I don't believe that biasing has to due with the heads so much as with the oxide used in the tape. I believe the bias signal "shakes" up the domain in the oxide so that a higher frequency signal can be recorded without having to have more amplitude. The bias signal should be adjusted for different brands and types of tape. --Dale | |||||
| 105.3 | JAKE::ROBERTSON | Wed Apr 10 1985 13:23 | 12 | ||
Well, it appears that my memory did me in again and that some of the items I have written about biasing were in error, sorry. After refreshing my memory about biasing it appears that response number 1 is correct. In some more detail the bias signal is similar to the signal sent to the erase head to erase tapes but at a much lower amplitude and in fact causes some erasure of high frequencies being recorded. Equilization is applied to compensate for this inherent erasure both during recording and playback. The main reason for using a bias signal is to reduce distortion during the recording process. --Dale | |||||