What determines sound quality?

Answer 1

Some of the aspects of the sound quality:

- Sampling rate (digital). It is the frequency of taking the snapshots of audio signal (since analog signal has infinite points in any given time range, we must take some amount of information out of it as digital storage is finite). The sampling rate is connected to harmonics (additional components of sound not present in original sound) which are artifacts of sampling. The lower the sampling rate, the bigger the harmonics are.

- Entropy (analog). For instance dust and scratches on the surface of the gramophone record or its needle while reproducing or similar on microphone during recording.

- Signal to noise ratio (analog, digital). The noise can come from variety of sources - background (ambiental) sounds, multiple mathematical round-ups (digital systems, precision, adda conversion) which can accumulate to form noticeable sound artifacts, recording material imperfection (pureness, homogenicity), etc..

- Isolation. Level of environmental effects like reverb, delay or echo. In digital systems one can synthesize artificial sounds without any of the mentioned effects but in nature no sound can be entirely isolated from its environment. If the thing that I am interested in recording is for instance speech, big reverb will influence perceived quality of the sound.

- Compression (digital). Today we have all sorts of sound compression - mp3, mp4, ape, ogg, mac, flac, wv, etc... Those can be separated into loosless and non-loosless codecs. The later will remove certain components of the original sound which is then lost (for instance higher frequencies are usual targets as human ear tend to hear less of them as it ages, which means that age also influences perceived sound quolity).