TAPE GUIDE (Jun. 1983)

Home | Audio Magazine | Stereo Review magazine | Good Sound | Troubleshooting


Departments | Features | ADs | Equipment | Music/Recordings | History

Too Much High End

Q. Some time ago I sent my tape deck to a company to have it tuned up and indicated that I would like to see the high end brighter. Now the highs seem unnaturally bright. I plan to have a local shop readjust the deck. Please tell me what adjustments are involved so that I may speak intelligently with the shop personnel.

-Joseph Lacerenza, New Rochelle, N.Y.

A. To brighten the response of your deck, the company may have done one or more of the following: (1) de creased the amount of bias used in recording; (2) increased the treble boost employed in recording; (3) modified the playback equalization.

Your deck should be aligned with respect to the tape that you plan to use in the future. First, playback equalization should be adjusted for flat response when playing a test tape. Then bias and recording equalization should be adjusted for the optimal combination of low distortion and flat response on a record-playback basis; or in your case, perhaps with a slight high-frequency emphasis.

Disc-Dubbing at Half Speed

Q. I propose to play a digitally mastered phono disc at half speed (16 2/3 rpm), dub it onto my cassette deck at 1 7/8 ips, and play the tape at 3 3/4 ips.

What changes are necessary in the phono playback and tape record equalization curves? Please provide me with new time constants.

-Ralph Morgan, Wahiawa, Hawaii

A. From the tape side, I see no merit in recording a cassette at half speed. Frequency problems in tape recording are functions of recorded wave length-, if you halve both the frequency and the tape speed, this will not change. You may even add a problem, because wow and flutter tend to be greater at 1 7/8 ips than at 3 3/4 ips. [On the phono side, you may solve high-frequency tracking problems, but you'll raise the frequency of any rumble, wow and flutter in your turntable, and of your arm/ cartridge resonance. -I.B.]

If you insist on going ahead, do not change the 3 3/4 ips playback equalization; keep that standard. Since record equalization is not standard, but is adjusted so that tapes made on that ma chine will have standard playback characteristics, it is impossible to tell you in advance specifically what changes to make in that. As a starter, lower the frequency at which your 1 7/8 ips record-EQ treble boost begins.

The RIAA phono playback curve has maximum bass boost at 50 Hz (a 3,180uS time constant), declining towards 500 Hz (318 1.13), plus a treble cut commencing at 2,122 Hz (75 uS).

If all frequencies are halved by playing a disc at half speed, the turnover frequencies must also be halved, by doubling the respective time constants to 6,360, 636 and 150 µS.

Recording vs. Playback Levels

Q. When recording, I keep the peaks within -3 to 0 dB on the record level meter. However, during playback the meter goes well into the red above 0 dB. Although no distortion is notice able during playback, I am concerned about the discrepancy between the meter readings in recording and in playback.

-Robert Rigsby, Richmond, Va.

A. As long as you hear no distortion, there appears to be nothing to worry about. Some brands and types of tape are "hotter" than others; that is, they have a relatively high output for a given input. The manufacturer of the cassette deck cannot foresee which tape you will be using. If your tape has higher than average output, this can drive the meter into the red during playback.

Your meter might be mis-calibrated with respect to output readings. Some decks have an internal control for adjusting playback calibration so that the meter gives about the same reading in playback as in recording. If your deck contains such a control, a competent technician can easily adjust it for the tape of your choice.

Reducing Only Noise?

Q. Can any noise-reducing unit operate without losing a lot of sound?

-August Yirsa, Brookfield, Ill.

A. When using Dolby NR, there may occasionally be some loss of the very low frequencies say, below about 30 Hz or so, according to some reports. When using Dolby or dbx NR, there may be some loss of the very high frequencies-say, above 15 kHz or so. But all this tends to vary among decks.

Dynamic-filter noise reducers (such as the Burwen or DNR systems), or autocorrelators, can also cut high frequencies, depending on the setting of their sensitivity controls. For the best compromise between noise reduction and high-frequency loss, these systems should be readjusted with each change of program material.

Dying Left Channel

Q. When I turn on my cassette deck and begin recording, everything is tine, but after about 45 minutes nothing at all works on the left channel. If I turn off the power for a few minutes, every thing is okay again. What could be the problem?

-Julio Poma, Bronx, N.Y.

A. There may be a poor solder joint in the power supply to the left channel.

As temperature varies according to whether the cassette deck is on or off, the joint may cause the connection to be complete or incomplete. Another possibility is a faulty switch or component which doesn't work properly when it's warmed up.

(Source: Audio magazine, Jun. 1983, HERMAN BURSTEIN)

= = = =

Prev. | Next

Top of Page    Home

Updated: Wednesday, 2019-06-26 2:16 PST