It won't destroy it. It may degrade it. Recording engineers use compression/expansion algorithms routinely. But if you're an audiophile, it's very unlikely that you'd use one of these, anyway.
OK, "destroy" was probably too strong a word. I agree there is nothing inherently wrong with companding as part of audio engineering, especially for "modern" music.
Mainly, I wanted to point out the downside of devices like this, that their effects on music, particularly Classical (and some Jazz, etc.), is likely to be quite unfavorable.
@BoloMKXXVIII: They have to process it, that's what volume leveling is! Basically, a compressor is a feedback loop (measure power, adjust volume, measure...) that targets a (more) constant audio power. So, when the device sees low power for a while, it will up the volume. When it sees high power for a very short while (2ms, according to the spec), it will lower the volume. That alone is audio processing. The hiss removal is needed, because otherwise intended silence will be amplified, producing a quite notable hiss. The equalization is probably to help the feedback loop more closely approximate perceived loudness (which differs from audio power substantially; the ear's response varies substantially by frequency).
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