August 29, 2005

I like to listen to my old vinyl records from time to time, but on all of my LPs I can hear distortion in the form of a "ragged" sound quality in the last song on a side, particularly during loud passages. Q: Does this have anything to do with the distance between grooves toward the end of a disc?

Anthony

A: When vinyl died as the primary format of recorded music, this effect was one of its least-mourned aspects. It’s called "inner groove cramp," among other things, and it does have something to do with density -- not the density of the grooves across the surface (called pitch), but rather the packing of data within the groove.

A CD rotates within a steadily varying range of 200-500rpm, starting at the inner groove and proceeding out to the rim. An LP, on the other hand rotates at a constant rate of 33 1/3rpm, beginning at the rim and finishing up in the inner grooves. This means that the linear speed of the groove at the outer edge is much faster than it is near the label -- more than twice as fast, in fact. Nevertheless, the same amount of elapsed playing time must be contained in a single rotation in either place, which means that the musical information is crammed closer together in the inner portion of the disc. The twists and turns of the groove there are thus much closer together, and the "corners" are much sharper; the effect is worse if the levels are high -- as they often are, for instance, in classical music that ends with a crescendo.

The best phono cartridges can negotiate, or trace, these curves with relatively little difficulty, but lesser designs often can’t hack it and mistrack near the end of a side -- the stylus loses contact with the groove for a moment, then crashes back down. This not only sounds terrible, it can damage a record permanently.

Your LPs may already be wrecked, but for any that have escaped this sort of damage, one solution that often works is to crank up the stylus pressure a bit. It may seem intuitive that the lighter the force the stylus exerts on the soft vinyl surface, the less the potential damage, but in reality it’s better to have slightly more friction than to mistrack.

If you still have a copy of your cartridge’s specifications, try setting the stylus force a bit above the recommended amount, if it’s a single number; if you’re given a range, set the force at the top of the range. If you don’t have these numbers, and assuming things are well behaved at the beginning of the disc, try adding about half a gram to the force you now use.

...Ian G. Masters