As well as the bit rate of the encoded file, the quality of MP3 files depends on the quality of the encoder and the difficulty of the signal being encoded. For average signals with good encoders, some listeners accept the MP3 bit rate of 128 kbit/s and the CD sampling rate of 44.1khz as near enough to compact disc quality for them, providing a compression ratio of approximately 11:1. MP3s properly compressed at this ratio can achieve sound quality superior to that of FM radio and cassette tapes, primarily due to the limited bandwidth, SNR (signal-to-noise ratio), and other limitations of these analog media. However, listening tests show that with a bit of practice, many listeners can reliably distinguish 128 kbit/s MP3s from CD originals; in many cases reaching the point where they consider the MP3 audio to be of unacceptably low quality. Yet other listeners, or the same listeners in other environments (such as in a Corvette with "husky" exhausts or at a party), will consider the quality acceptable. It is important to note that quality of an audio signal is subjective. A given bit rate suffices for some listeners but not for others.
Good encoders produce acceptable quality at 128 to 160 kbit/s and near-transparency at 160 to 192 kbit/s, while low-quality encoders may never reach transparency, not even at 320 kbit/s. In data compression or psychoacoustics, transparency is the ideal result of lossy data compression. If a lossily compressed result is perceptually indistinguishable from the uncompressed input, then the compression can be declared to be transparent. In other words, transparency is the situation where compression artifacts are nonexistent or imperceptible.
However, transparency, like sound quality, is subjective. It depends most on the listener's familiarity with artifacts, and to a lesser extent, the compression method, bit-rate used, listening conditions, and listening equipment. Despite this, sometimes the general consensus is formed around roughly what "should" be transparent for most people on most equipment. Using MP3 audio, it is popular to assume that files with 192 kbps bit rate (44.1 kHz sample rate, 16 bit sample size) should be either transparent or close to transparent.
Storing MP3 Music Files
MP3 music files are in digital format, making them storable and transportable on an assortment of media, including the hard drive in your computer, on CD (particularly for C6 owners), and other removable storage media such as compact flash memory cards, USB flash drives, Secure Digital and MultiMedia Cards, as well as dedicated MP3 players that often have huge internal storage capacities. But how did this all come about, you ask? Good question. Here's the answer.