Bantam-size stereo products have taken two interesting turns. One is the small-is-fun type; the other part of an ongoing trend in compact high-quality speakers.

Billed as the world's smallest stereo cassette player is the Sony Walkman, which weighs just under a pound and measures 5-5/16 by 3 1/2 by 1-3/16 inches. It runs on two "AA" alkaline cells and it also may be powered, via adaptors, from car electrical systems, a rechargeable battery pack or regular AC . It plays standard cassettes which are heard via bantam headphones that come with it, and a second headset also may be jacked into the unit. Supplied with carrying case and strap, the Walkman may be slung over the shoulder, fastened to a belt or even tucked into a large pocket. Price is $200.

Possibly more striking is the Bone Fone system, which packages a tiny stereo receiver in two housings that slip into washable covers that can be draped around the shoulders like a scarf. The whole system weighs 17 ounces -- about the same as a full-size bath towel -- and costs $70. It runs on four "AA" cells, and the listener hears the stereo via bone conduction, with nothing actually on or over the ears.

In petite speaker systems, there are some recent entries that claim unusually high performance for their dimensions. For instance, there's a new line from General Sound of Phoenix called Micron. Speakers in the 600 series measure 11 5/8 by 7 5/8 by 7 3/8 inches, weigh 14 1/2 pounds and boast overall response from 35 Hz to 25,000 Hz.

From France, via Acoustique 3-A International of Montreal, comes the Andante speaker, 18 by 12 by 8 inches. Its weight (48 pounds) and price (over $800) reflect the fact that this speaker includes a built-in bass amplifier that drives the woofer through a feedback system. Rated response is from 25 Hz to 30,000 Hz. A very late Belgian entry is the KM-52, which measures 14 by 10 by 9 inches and is said to furnish sound levels up to 105 dB with bass down to 38 Hz.

Those skeptical about deep bass from such small speakers should consider how headphones manage to provide bass from diaphragms only 2 1/2 inches wide. Feedback

Q. I am planning to tape-record my church choir and organ playing over the church's sound-reinforcement system. I have set up a graphic equalizer in this system to smooth the overall response, but someone suggests I also use a parametric equalizer before the signal goes onto the tape. Would this be "overkill" (and in church yet)?

A. Not necessarily. It depends on how fussy you want to be. The graphic equalizer can "tune the room" to your satisfaction, but you may run into unwanted response effects such as a remote-sounding or overly bright-sounding section of the choir. The parametric equalizer can compensate for those effects without upsetting the balance achieved by the graphic equalizer.