Hi-Fi Sound on Hi-Fi VCRs (Sept 1988)

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by JOSEPH GIOVANELLI

The first home video recorders had terrible audio, with poor S/N (even with Dolby NR) and limited frequency response. However, it wasn't long before some sharp engineer realized that an audio signal could be imposed on an FM subcarrier and recorded along with the video information.

The result was to turn VCRs into audio recorders with very good specs. I've been using Hi-Fi VCRs for audio recording for some time, and I've learned a few things which may be helpful to readers who wish to use their VCRs for audio, or who are trying to make a decision as to which VCR to buy for this purpose.

These VCRs record sound on conventional longitudinal, or linear, audio tracks (though usually just monophonic ones), at the same time they record it on their FM-subcarrier tracks. This allows compatibility with conventional VCRs, which can not play back Hi-Fi audio tracks. Having linear tracks on Hi-Fi VCRs also allows you to make an audio overdub (if the VCR has that function), since the Hi Fi tracks of such decks cannot be overdubbed without erasing video information.

Hi-Fi audio is laid down by the video head drum, which requires sync pulses to keep it aligned with the proper tracks on the tape. With out sync, the recorder will behave erratically, much like a television that suffers from sync problems. When recording video, the sync pulses can be obtained from the composite video signal, but the VCR must provide its own sync when it is used as a stand-alone audio recorder. Most manufacturers of Hi-Fi VCRs have made provisions for this.

Because a VCR's Hi-Fi audio channels are FM, the frequency response of these channels s unaffected by tape speed, and the wow and flutter associated with conventional, longitudinal tracks is inaudible, even at the slowest speeds.

However, the audio which is recorded on the standard linear tracks will suffer from wow and flutter and from limited frequency response, especially at slow tape speeds.

HI-FI Editing

There's more to re cording than recording! The open-reel recorder makes editing quite easy. By marking the tape in the appropriate places, unwanted sections can readily be cut out and the tape re-spliced. Sections from one point in the tape can be moved to another by similar methods.

But with videocassettes, splicing is not an option. It would be al most impossible to cut the tape without producing glitches in the audio, video, and sync, which sends a VCR into a frenzy, and the splice might catch on the VCR's rotating heads, damaging both tape and heads.

A good open-reel or cassette recorder will usually have a pause control, which allows the tape to be stopped and started with the capstan motor running at operating speed. Thus, one can almost instantly start up or stop the tape.

Usually, the pause control can be actuated without introducing clicks.

You won't find this feature on VCRs-a point to remember if you're thinking of using one as your primary audio deck. Because of the way a VCR handles tape, it takes time for the machine to get the tape back up to speed and to reestablish sync; only then is audio muting can celled, either for recording or for play back. If the tape is set into motion from stop mode, still more time is lost while the threading mechanisms extract tape from the cassette.

There is another peculiarity related to the recording process. Because of the need to maintain sync, pressing the pause button does not merely stop the tape in the usual manner. Rather, the tape backs up a distance so it can get up to running speed and lock sync before recording starts. Thus, if you stop a recording just at the end of a passage, part of the recording will be lost. You must learn to wait a bit and not be too quick on the draw. If you plan to copy one tape to another straight through, however, these pause problems will be of no consequence.

Speaking of copying, I was running out of space to store all of my open-reel tapes and my collection of 78-rpm discs. I transferred all of this material onto Hi-Fi videocassettes. I used a VHS deck, running it at its slowest speed. Using T120 tapes, I could put approximately six hours of programming on a single tape. Can you imagine how many 10-inch 78-rpm discs I fit onto a tape? Indexing

If you store large amounts of information on a single tape, the means must be available for locating any de sired section. The simplest solution is to set the tape counter to 0000, or 00:00, at the start of a new tape. At each important point in that recording, mark down the counter reading and what programming occurs there. Such a notation might read: "173: Start of Music for Dreaming, Paul Weston and Orch." You might break down your index further, to show the start of each selection on an album.

I suggest that you arrange your material in logical units-logical to you, at any rate. This means that you can't use just any selection of the proper length to fill the last few minutes of the tape.

You may sometimes wind up with some blank space at the tape's end, when the only selections that logically belong on the tape are too long to fit in the remaining space.

All your indexing information could be entered into a notebook, but if you have a computer, you might want to enter that information into some kind of data-base program. By arranging your material into logical "fields," you then can use appropriate search criteria to find specific sections of your tapes.

One of the many advantages of a computer is that it can search through in formation for many tapes simultaneously, provided your records and search criteria are properly organized.

Be sure to make backups of your data though, and retain your original notes.

I also index my Hi-Fi VCR tapes sonically, on my VCR's linear audio tracks.

After recording and indexing music or other selections, I use my VCR's "Audio Dub" function to record announcements on the linear track. (This function does not affect the Hi-Fi track, as I mentioned earlier.) My announcements might include the name and timing of selections, or an audio "reading" of the album's liner notes.

Taking this idea a bit further, I add a low-frequency tone to the linear track just before the end of each selection on the Hi-Fi track. Then, with the deck in fast-search mode, I listen for these tones, which are easy to hear because their pitch increases as the tape speeds up.

To the experienced VCR user, this may seem impossible, since almost all decks mute the audio output when in fast-search modes-as mine did, until I modified it. On most VHS decks, this is impossible to do in fast-wind modes, since the tape is pulled back into the cassette before the wind begins. I have not worked with Beta, but think that the tape may be close enough to the heads in fast-wind to allow this audible cueing technique. (You should make the modifications I mentioned only if you have a complete service manual for your model VCR, under stand the circuitry, and are very skilled with tools. If not, don't try it!) The reason that you hear no signal in search mode is that the audio from both the linear and Hi-Fi tracks is muted, even though the tape is still in proper position to play these tracks.

The muting is controlled by the micro processor, which governs the operation of the entire VCR. This micro processor senses when sync is established and removes the mute.

In my equipment, at any rate, I only needed to cut one circuit foil leading from the microprocessor to the muting circuit, which did not affect muting during recording startup. I found so many layers of muting and error checking that it was difficult to make the right choice the first time; I literally had to cut and try various possible points in the circuit until I located the one I needed.

When I search forward or backward, I hear the sound of the linear track chattering away. Where the track is blank, I just hear tape hiss. I can also listen to the chatter on the Hi-Fi tracks by resetting the deck's audio selector switch. This sounds similar to the fast-search modes on CD players. You might recognize music, but it will sound broken up, robbed of dynamics and distinctness. Still, listening to this is not as unpleasant as listening to the speeded-up chatter on the linear tracks.

Un-muted audio is a mixed blessing.

When you use your VCR in the normal way, you will hear some strong clicks when you begin to play a tape, whether from a dead stop or from pause. You also will hear the unit switch between linear and Hi-Fi tracks as sync is established. I found both the clicks and the switching very annoying, and over came the problem by adding a simple toggle switch to the rear panel of my machine. This switch restores the circuit foil to normal in one position and opens it in the other. If your machine requires more than a single cut, however, you will need a more elaborate switch.

What I have said about overdubbing the linear tracks and listening to them at high speed should also apply to people who use PCM encoders to make digital recordings on VCRs, whether they use conventional or Hi-Fi decks. I doubt, however, that one could listen to the digital tracks at high speed.

Until now, I have mentioned only the audio capabilities of Hi-Fi VCRs. Nevertheless, they can record video along with audio. As you record sound through the deck's audio input jacks, you can simultaneously use the video inputs to record visuals from a camera or another VCR. If your deck has a "Simulcast" switch, which allows the audio and video inputs to be selected independently, you can also record video from the VCR's built-in tuner.

(This does not apply, of course, to recording with a PCM encoder, since the PCM information occupies the video tracks.) So why not add video to your audio? Perhaps the video could show the composer or musician you are hearing on the audio tracks, or maybe notes you've written describing the music. If you put typed or printed notes on screen, keep the letters large or they may not be readable. Try about 15 lines of text, about 60 characters per line, to see how legible it looks on your screen. And leave some white space around your text when you shoot it, to make sure none of the words get cropped off the edge of the screen. All video accompaniments must be care-fully planned, because the audio and video must be recorded simultaneously. On today's videocassette decks, you cannot "punch in" directly from play to recording.

Controlling Level

A few words of caution are required before you buy a Hi-Fi VCR. While most offer both manual and automatic recording-level controls, some machines do not allow manual level set ting. Since this is most often true of portable VCRs, stick with tabletop models if you do not need portability.

They are cheaper and more likely to provide manual control of recording level.

Nevertheless, when I needed a second VCR for dubbing, I found it advantageous to get one capable of battery operation. I then discovered that all is not lost as far as controlling audio levels on a portable VCR. The trouble with automatic level controls is that they compress the signal. Fortunately, if you don't feed in signals beyond the level that produces a 0-VU recording, the effects of automatic level circuitry won't be significant. I therefore arranged to drive my portable VCR's audio inputs from a mixer which had its own level meter, and determined what output level from this mixer would pro duce 0 VU on my VCR.

I have encountered one problem with my portable machine which I have not completely solved. Hi-Fi VCRs use "compansion" to increase their S/N ratio. There appears to be a nonlinearity in this compress/expand system, and it is most noticeable when recording extremely low-level audio signals. As a result, I am occasionally conscious of background sounds being modulated by the program's changing dynamics.

If the program source is an open-reel tape, the level of tape hiss will vary slightly. If the source is a live performance, ambient sounds in the room can sometimes change just a bit in level. Fortunately, I cannot detect this condition most of the time. I found that I could improve matters by changing the IC responsible for my portable VCR's recording compression. Experiments demonstrated that the playback expansion was not responsible for this problem.

By comparing notes with a couple of my friends who use Hi-Fi recorders, I found that they had experienced the same problems, mainly with portable equipment. Because my desktop unit does not suffer from this "companding" problem, and because my portable machine plays back fine, I use the portable to play tapes while making coves of these tapes on the desktop unit.

As with any important recording, it is well to stay clear of bargain tapes.

They will prove not to be a bargain if, after a few plays, you find tracking problems. These will manifest them selves in the form of odd flutter, which can usually be corrected by adjusting the tracking control.

It was necessary for me to point out some negative aspects of Hi-Fi VCRs (VHS, at any rate) in order to present a balanced picture. Nevertheless, I think you will discover that if you are careful, you will enjoy many happy hours of recording and listening.

(adapted from Audio magazine, Sept. 1988)

Also see: The March of Technology: Analog Tape Home Recording (May 1997)

Celebration of Audio's Earliest Years

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