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"Single" and Album Sound

Q. Why do 12-inch "singles" sound so much better than LPs or CDs? Is it because of remixing, re-equalization, the pressing format, or what? Will this same standard become available on CDs?

-Guy Martinez, Boca Raton, Fla.

A. It is difficult to say why "singles" may sound better than albums do. You may have hit upon some of the possible reasons in your question, however.

When 12-inch "singles" first appeared, many were recorded at 45 rpm. This allowed for better high-frequency response, because it made the recorded wavelengths of treble frequencies longer, in relation to the play back stylus' tip radius, than they would be on a disc playing at 33 1/3 rpm.

Because there's less music on each disc, the 12-inch single's groove need not extend as far toward the center of the record as an album's groove. Since wavelengths become smaller as groove diameter decreases, this also keeps high-frequency wavelengths longer than the playback stylus' tip radius, allowing the highs to be well re corded, even on 33 1/3-rpm discs.

Having less music on each disc also means that the grooves can be spaced more widely. Heavy bass, which produces wide swings of the cutting stylus, need not be restrained to keep that stylus from cutting into adjacent grooves and spoiling the record.

All of this gives the mastering engineer greater freedom to add both highs and lows to the single. Even when the original album was well re corded, it is sometimes possible to spice up the single version.

There are no similar comparisons possible between CD albums and CD "singles." Unless the engineer equalizes a brighter "single" or one containing more substantial bass than he did for his album, the CD "single" and al bum will sound exactly alike.

Hum from a Turntable

Q. I have been having problems with an old turntable. Most of the time I can hear a low hum during quiet pas sages or between selections. Because the hum frequency is in the region be tween 100 and 190 Hz, attempts to remove it by means of an equalizer are not practical, because of the loss of bass which would also occur. I have tried tightening all connections and grounding, and some adjustments to the cartridge connections helped for a short while. What might cause this hum, and how can I stop it?

-Ryan Tamares, San Bernardino, Cal.

A. Hum is usually defined as noise caused by leakage of the a.c. line frequency (or its first harmonic) into the signal. You apparently are not getting 60-Hz line-frequency hum, and 120-Hz hum (which does lie within the frequency band you mention) is usually heard as more of a buzz. So I have to wonder whether this is really hum at all.

One of the most common causes of a.c. hum is poor phono signal or ground connections, which you did say you checked. Considering that some temporary improvement occurred when you worked on the connections to the cartridge, we can't rule out an electrical reason for the hum.

Let me briefly mention some areas that usually bear exploring.

First, check the terminals on the cartridge to be sure they are clean and free of oxide. Be sure the lugs which slide over these terminals are tight If they slide on too easily, tighten them by gently squeezing the lugs with small pliers. Next, spray contact cleaner into the tonearm at the point where the shell makes contact. Clean the contacts on the shell as well. If your arm has a detachable phono cable, make sure its connections are clean and tight. Check the ground lead, which should normally go between your turn table and preamp (but note that in some systems, where ground loops exist, hum will be lower if the ground lead is disconnected).

Finally, check the phono connectors which plug into the audio system. Be sure they are clean and that their skirts are tight, so that they make intimate contact with the grounds on the audio system. If they are loose, squeeze them with pliers just enough that they fit very snugly when reconnected.

In your case, however, it is likely that the hum is not electrical. It may instead be a mechanically produced form of rumble. This may be caused by hardening of the motor shock mounts, in which case the mounts should be replaced. If spare mounts are no longer available for your old turntable, you may be able to find some rubber grommets which can do the job. When you remount your motor, be sure no part of the turntable assembly touches the rest of the turntable base.

If your turntable has an idler pulley interposed between its motor shaft and inner turntable rim, replacing it may cure your problem. Also, use light oil to lubricate the shaft on which the idler rides; this sometimes helps, even if a replacement idler can't be found.

If your turntable shaft rides in a well, place a couple of drops of light oil into the well before replacing the turntable spindle. Some old turntables employed ball-bearing assemblies; lubricate these with light grease. Be sure to take care when disassembling the turntable so that you can put it all back together without losing any of the ball bearings.

Acoustic feedback is another possible cause of your problem. If it is, the hum will disappear when you shut off your speakers and listen through head phones. Possible cures would then include attention to the mounting and lo cation of your turntable and speakers. Often, moving the turntable just a foot or two will alleviate feedback.

One last possibility is that some part of your turntable is mechanically resonating at a harmonic of the line frequency, either 120 or 180 Hz. If so, you'd hear this even when the amplifier was off. To cure such a problem, you'd have to track it through your turntable mechanism to find the source, then tighten or add damping materials to the offending parts.

CD Players with Three Lasers

Q. My CD player has three lasers. What does each of them do?

-Name withheld, Detroit, Mich.

A. There is really just one laser, but its light is split into three beams. The center beam reads the data to be de coded. The other two beams read where the laser is in relation to the adjacent tracks. These two outer beams feed information to the servo, which then keeps the central beam on track.


(Audio magazine, Oct. 1988, JOSEPH GIOVANELLI)

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Updated: Monday, 2020-01-27 9:23 PST