AUDIOCLINIC (Sept. 1991)

Author's Note:

Keep those letters coming! I'll do my best to answer them.

Some of you need a fast reply, but unfortunately this is not possible. I do not work in the magazine office; letters must be forwarded to me. Also, quite a bit of time can pass before I can do the research for any given letter.

It would be helpful if, as you write, you let me know if I have permission to use your name along with your question. If you do not grant permission to use it, I will still use your question--signing it "Name withheld." Now it's time to get to work!

-J.G.

Equalizing During Record/Playback

Q. I usually record cassettes with my equalizer out of the circuit and play them back using the equalizer. What advantage would there be to recording with the equalizer, and when would be the best time to use it?

-Ernie Poggie; West Babylon, N.Y.

A. If you wish to make a tape that will sound as close as possible to the original program source, you would probably not use the equalizer except to compensate for anomalies in the frequency response of the recorder.

You might also use the equalizer to reduce the treble before recording any program material whose treble is so strong that it might cause treble saturation on the tape--a sound much like that of a mistuned AM radio. You could then use inverse equalization in playback to bring the treble back to normal.

On the other hand, if the program source's treble is too soft, you might want to boost it during recording rather than compensating for its lack during playback. When you boost treble during playback, you are also increasing the amount of audible tape hiss. Thus, boosting treble during recording avoids this problem for the most part.

It is helpful if your tape deck is capable of simultaneous recording and playback, because this makes it possible to hear any treble saturation or tape hiss without having to make numerous tests, rewinding the tape and playing it back.

(Editor's Note: You can also use your equalizer in recording to pre-equalize tapes for special purposes, such as to compensate for problems with your car's acoustics. However, such tapes will then sound a bit odd when used for more normal purposes. And remember that excessive boosting of any frequencies, especially high ones, in recording can cause saturation. –I.B.) More on Removing Vocals I'd like to add to the answer you gave, in the November 1989 issue, to Tom Tuttle's question on removing vocals from recordings. You suggested using a mixer for this. However, there's another way, which involves equipment more likely to be found in home sound systems.

I assume first that the lead track he wants removed is monophonic--that is, center-channel information. I have had good results by using the Dolby Pro-Logic surround sound decoder incorporated in my receiver. I set the receiver to "Dolby Surround Pro-Logic" and turn the center-channel volume fully down. All that remains of the lead is the echo, or reverb, heard in both the left and right main loudspeakers (and in the rear loudspeakers, of course). These speakers can be switched off as necessary. The best part is that what remains of the recording is in stereo! Any Dolby Pro-Logic surround decoder or any decoder with a center channel output should provide the same result. Mr. Tuttle wouldn't need to rerecord the stripped-down version, and he can practice by using the original as run through the decoder.

When it comes time to make a recording, the left and right output jacks of the decoder can be routed to the appropriate inputs of his recorder. The stereo information will be present here, minus the center channel. Presumably, when he makes this recording, he will be dubbing his voice or instrument onto the processed recording. By removing the intermediate recording step, better fidelity will be obtained.

The small amount of echo or reverb that remains in the main loudspeakers after processing should not be too annoying--at least not for the purposes of practicing. In most cases, once the new part has been dubbed in, the echo of the old part will be masked and so will not be heard.

-Greg Lawrence, Darien, III.

Distortion on Phonograph Records

Q. Is there any way to distinguish between distortion caused by the cartridge's mistracking and distortion from damage that has been done to the disc? Assuming the record surface to be okay, would there be any point in upgrading a cartridge or turntable when I could replace several records, which are most definitely worn, with CDs for the same money?

-K. Nelson Harper, Fort Smith, Ark.

A. Play any discs which seem to have distortion on other phonographs. If the disc plays well on other machines, your system is to blame and corrective remedies can be taken. If you examine a disc carefully, sometimes you will see a gray color. This often indicates that the disc was indeed damaged by either a defective stylus or one which was set to track with entirely too much force.

Assuming that the discs are fine on other systems, check your system to see what corrections can be made to it. First, is the stylus damaged? If you accidentally dropped it onto the turntable or whatever, it could be chipped or its shank could be bent. On the brighter side, it may just be that all you need to do is increase the tracking force. It is usually best to track at the heavier end of the cartridge's recommended tracking force range, rather than at the lighter end, to avoid distortion during loud passages. Reducing distortion this way will also reduce record wear. You should also check the anti-skating force. Be sure to set it as close to the proper setting as possible.

Styli with low compliance will have problems tracking highly modulated passages regardless of tracking force.

The obvious cure for this is to replace the cartridge with one whose stylus is compliant enough to track your records. Because phonograph records are disappearing, you will want to be kind to them so that you can enjoy many quiet, clean plays. You should replace any damaged discs as soon as possible, while they may still be found.

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(Source: Audio magazine, Sept. 1991, JOSEPH GIOVANELLI)

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