The phrase "plain sound" is correct and can be used in written English.
Example: The violinist's performance was flawless, her fingers dancing gracefully over the strings to produce a pure and plain sound.
The POG2 just plain sounds better, thanks to an enhanced algorithm that delivers a more focused and in-the-pocket harmonic performance.
The expert and irony-free minimalism of "Jim the Boy" gives it the plain, wholehearted sound of a book for young readers.
There are only so many ways to make a plain bagel sound different from another plain bagel.
It would happen in total darkness on the abyssmal plain (which sounds quite dreadful) or the Charlie Gibbs fracture zone (who was he?).
To the consumer of 24-hour news, steeped in images of conflict and war, that may sound plain wrong.
He made that kind of close legal argument, ornamented by bald plain speech, the sound of liberal rhetoric.
I never resort to the glottal stop, not least because it would sound plain daft down here in Sussex, where none of the locals uses it either.
Some of the book's prescriptions are now esoteric or antiquated (the hip bath? The electric light bath cabinet?) and some sound plain awful (the tepid sponge, the salt glow, the acid enema).
The latter sections of her pieces often bring apparitions of rare, pure beauty — plain intervals that sound like harmony reborn, liminal melodies that disappear the moment they are heard.
A lot of the cakes and pastries sound plain, but plenty of them are complex and wonderful, such as the sage-walnut roll, or that apple tartlet, which tastes more like apple than some apples do.
