How much loss can you hear? Much depends on two factors: who you ask and how much is lost.

Paul McGowan writes:

Computer audio can be hard to understand. I know this because I get so many questions from our customers. The (seemingly) most misunderstood terms are lossy and lossless, compressed and uncompressed.

For starters, how many of us get an uncomfortable feeling when we hear our music’s been compressed? It’s like hearing your food was frozen; it’s rarely as good as fresh when thawed. Messing with pristine musical content in any way, shape, or form, surely can’t benefit the sound. The best we can hope for is untouched, unmolested.

We compress music to save disc space. Some compression schemes take half as much space, while others a tenth, even one hundredth in some cases. But all compression schemes are not the same. Some throw away “unnecessary” bits of music to conserve space, while others sacrifice nothing.  The names for the two types of compression, lossy and lossless, describe which loses data and which does not.

Lossy schemes include MP3, AAC, Dolby Digital, Ogg, and WMA. Lossless formats are primarily FLAC, and ALAC. File names like WAV and AIFF are not compressed at all. One everyone’s interested in as of late, MQA, is compressed, certainly, and uses a combination of both lossy and lossless to achieve its reduction in space. The designers claim to wind up with lossless if a decoder is used, a claim I have no reason to doubt.

How much loss can you hear? Much depends on two factors: who you ask and how much is lost. High bit rate MP3 can sound awfully good to most people, even on a decent system. Though, when you listen closely to your well know pieces, and on a high resolution audio system, the losses are evident: subtle details, low level harmonics in particular. But if you ask some sound engineers, reasonable levels of MP3 compression are inaudible. They have double blind tests to prove it too. Of course, these are the same guys who can’t hear differences in wires, formats or electronics, for the most part.

Lossless? Is it really lossless? There again we have several definitions. If, by lossless, you mean bit perfect, then yes, lossless files (after decoding) are identical to uncompressed files. But, if you mean to ask, do they sound differently, then that’s a much debated question.

To my ears a FLAC or ALAC file that’s been uncompressed, decoded, and stored as a WAV or AIFF file before being played, sound identical to the original. FLAC or ALAC files that are uncompressed, decoded, and played in real time do not sound the same.