After spending the better part of an evening compiling a mix tape for your car, it's time to see if these songs suit your morning commute. So you rev up the engine, crank the car stereo, and head for the highway.

Everything seems fine at first. In fact, it's so good to have new tunes in the car that you're almost glad to be going to work.

Until the fifth song in the mix comes on, that is. Hearing it, you realize you've made a terrible mistake. It's got the wrong mood, the wrong groove, the wrong everything.

In short, it's got to go. Trouble is, that means another long night with the stereo, because the only way to drop track No. 5 from the mix is to record over it -- which will probably mean re-recording the rest of the cassette.

Unless, that is, your "cassette" is actually a MiniDisc, in which case you can delete the track with the push of a button. Not only will there be no tell-tale gap where the old song used to be, but you can easily add a new song to the mix -- and place it anywhere in the running order without rerecording the rest of the disc.

It's a mix-taper's dream.

A fully digital recording system, MiniDisc packs 74 minutes of recording time onto a disc that's smaller than a 3.5-inch floppy disk. Moreover, it's completely rerecordable, allowing the user to re-dub the disc up to a million times (which is a thousand times more than even a rewritable CD can be re-used).

A MiniDisc (MD) can also do things that are simply impossible with other recording formats. For example, if you want to keep track of the song titles on a cassette mix tape, your only option is to check the cassette case -- assuming you were diligent enough to write down every song title.

Even then, you have no way of knowing which song, exactly, is playing, because the machine has no way of telling you.

Not so with MD. Not only does the format allow you to title every disc, so that the name will come up on the player's LCD display every time the disc is inserted, but you can name each track as well. So even if you've forgotten that track No. 7 on your "Summer Fun" mix is Sly Stone's "Hot Fun in the Summertime," your MD player never will.

Add in such features as track editing, random play and a mono mode that allows you to double the disc's recording time, and it's easy to see why MD is a home-recorder's dream. So why does all this seem like news?

Because at this point, MD is one of the best-kept secrets in stereo. Even though the format has been on the market since the beginning of the decade, it's not nearly so well-known or widely used as CDs and cassettes. Although major electronics chains such as Best Buy and Circuit City carry MiniDiscs, players and recorders, many department stores and general discount chains do not.

But that's beginning to change. In Japan, where major pop stars appear in ads for MD players, the format has all but replaced cassettes for young consumers. We're a long way from that stage in this country, but with sales of nearly a half-million units last year, MD players and recorders are clearly catching on.

"MiniDisc has firmly established its role as the ultimate replacement of the analog cassette," says Mike Fidler, vice president of home A/V marketing for Sony Electronics. As he sees it, MD is clearly "the digital audio recording format of choice."

Of course, Sony has a vested interest in the growth of MD, having introduced the format. But back then -- when MD was competing against Philips' now-defunct Digital Compact Cassette platform -- Sony was the only electronics company making MD players and recorders. These days, Yamaha, Sharp, JVC, Panasonic, Technics and Aiwa are also marketing MD machines, while Maxell competes with Sony for blank disc sales.

Moreover, there's a full range of MD gear on the market, from rack components to car stereos to tiny portables. There are MD multitrack recorders for home studio use and MD decks designed to work with PCs -- complete with MD-editing Windows software. Still, if you want to record digitally, why not go to a CD-recordable format? For that matter, why not just stick with the old, reliable audio cassette?

For starters, there are still several major inconveniences with CD-recordables. Not only are there two formats -- CDR, which allows the user to record the disc once and once only, and CDR-W, in which the disc can be re-written up to 1,000 times -- but some CD players will not read CDR-W discs. MDs, by contrast, can be rerecorded up to 1 million times, and will work in any MD player.

Another problem is that CDs record sequentially, meaning that if you want to add a track to the disc, you have no choice but to put it at the end. And as with cassettes, trying to swap out a track in the middle of the running order usually means rerecording everything after the change.

With MD, you can move tracks around regardless of when they're added to the disc. For instance, I have an MD called "Current Rotation," which consists of my personal songs-of-the-moment. When I want to update it, I scroll to the songs I'm tired of, punch the "edit" button on my MD recorder, and toggle over to "delete." Another click, and they're gone.

Next, I check the "time remaining" function to see how much space the deleted tracks have left me. Then it's time to record new tunes.

Although it's possible to record from an analog signal -- using the same RCA plugs that attach every other component in my stereo -- I prefer to use optical cable for MD recording. Not only does this provide a higher-fidelity digital feed to my MD unit, but it also allows me to use the "synchro record" feature, which automatically starts and stops the MD recorder at the beginning and end of each track. All I have to do is type in the track names, which can be done even as the track is being recorded.

While recording, the MD unit puts the new songs at the end of the disc -- but that's easily remedied. Scrolling to a new track, I hit the edit button again. This time, I toggle to "move," and the machine asks me where I want to put the track. If I choose "6," the song will appear after track No. 5 the next time I play the disc. Simple.

Granted, there are some drawbacks to MD. For one thing, the discs themselves are nowhere near as cheap as cassettes, going for $4-$6 apiece. Moreover, because MD is a digital recording format, it's prone to problems cassette players never have. A few weeks back, for example, my Yamaha MD recorder decided it didn't like my discs -- any of 'em. No matter what I put in the machine, the display read "disc error," and the disc was rejected.

Fortunately, the dealer was able to replace the offending unit, and all is well with the world. Even so, the worst my cassette decks have ever done has been to is eat an occasional tape.

But where MD truly won my heart was in the car. It isn't just that the sound is better than the old cassette player, or that I can fit two MDs in the space of one cassette, or even that I'll always know precisely what song I'm hearing.

What I like best is being in complete control. If I want to play the same song 15 times in a row, I merely hit the repeat button. If I switch discs during a drive, I no longer have to worry about having to rewind. And if I'm midway through a song when I park, I have the option of starting it at the beginning when I get back into the car.

Best of all, fixing a mix tape is no longer an all-night affair ' unless I have trouble deciding what songs to choose.