Merzbow’s sounds are often called "harsh noise." Which is fair: his tracks have no melody, no harmony, and often nothing like rhythm. They don't have hooks to remember; they don't have recurring themes or sounds. Even when a texture persists for several minutes, it's only a matter of time until it stops and is replaced by unrelated others. The sounds are very dissonant and contain high frequencies which most people find grating. Merzbow's tracks sound more like factory machines or explosions than like conventional music.
That’s the description of Merzbow commonly given; but it misses what makes him interesting.
Merzbow's works are free in ways that normal music can't be. They're dense with effects processing—flangers, phasers, filters, delays, distortion—more than even the most psychedelic of acid rock. They're constantly surprising; often one section ends, a few minutes into a track, replaced with a second section that has nothing to do with the first. The sounds from the earlier section never reappear. These are tracks that literally never repeat themselves, that move on without pause. There's no melody or harmony to tie them down: anything can happen at any point.
They're works about, in his words, "the ecstacy of sound itself." (http://www.esoterra.org/merzbow.htm) Sound itself, liberated from the melodic and harmonic structures that normal music uses. If you miss that—the incredible freedom of the sound, the almost gleeful exaltation of noise—Merzbow’s work is tedium or torture. But if you get that there’s nothing else like it.
Take a track like “Degradation of Tape,” from his album 1930. This is a timeline describing the track’s first 20 seconds:
0:00.06 A very brief (roughly 1/10 of a second) blast of shrill white noise begins the track, followed by a silence so short as to be inaudible.
0:00.2 A slightly lower blast of noise begins.
0:01.6 The noise takes on a pitched quality, sounding like a flange effect with extreme settings.
0:04 The volume very briefly drops to nearly zero. The previous noise stops and is replaced by a somewhat higher noise which sounds like a combination of an explosion and white noise.
0:05-6 There are several very muffled snare drum hits.
0:07 The snare drum loops rapidly, creating a sound similar to a machine gun.
0:08 The snare loop slows down, lowering its pitch.
0:08.9 The snare loop slows down again, even lower than before...
0:09.4 ...and again resumes the previous speed.
0:10.8 The snare loop (or some other loop; it is not completely clear) is repeated very quickly, to the point where individual hits can hardly be made out, speeding up quickly...
0:11.6 ...until the frequency of the loop is so high that it is audible. (That is, the loop is going so fast that the speed of its repetitions is creating a particular tone.)
0:12.7 The loop is lowered in pitch.
0:13.3 The loop is lowered in pitch again.
0:14.9 Certain higher frequencies are added to the sound of the loop. It is unclear whether this is due to another sound being added or due to some kind of added effects processing.
0:17 Again, new frequencies, or possibly the loop's pitch is raised.
0:20.7 The loop stops and is replaced by another noise
You could take any fragment from his work and come up with something similar in complexity and density of events. Note: there are almost no recognizable sounds. The track doesn’t divide up like a normal track would. But the sheer variety of sounds is staggering. At his best (and 1930 is certainly in that category) Merzbow is ceaselessly creative. Sounds change without any pattern; every possible frequency is tried, abandoned, and tried again. And still the sounds go on, in endless variation--a single track sometimes lasting an hour or more. The results are abstract but evocative, like Pollock canvases (it's not surprising that Merzbow studied painting before turning to sound). These are sounds you can get lost in, if you let yourself.