Fans of performers such as Madonna and Britney Spears, among many others, probably don't question the quality of the singing of their favourites. The singing sounds good on the recording and it sounds good when they see them live, but how far are you listening to the actual performer? Not much nowadays.
Since the 1990s, autotune has made massive inroads into the music business to the extent that many performers routinely expect their vocals to be put through 'the box' to iron out any imperfections: even a badly out-of-tune voice can be put perfectly in tune. In earlier times, artists would make multiple recordings of a song until they were satisfied with the result, but this is too much like hard work for some of today's stars, so when they're recording, their voices get far less use than their predecessors'.
When Louis Walsh of X-Factor was challenged that Cheryl Tweedy (as she was then) used autotune, his response was, in effect, so what? This is despite the fact that it is meant to be a programme to select the best new singers, but there was a strong public reaction against the news that its performances were routinely autotuned. We are told that X-Factor no longer uses autotune.
I have been going to folk clubs for more than 40 years and I am used to completely unplugged, unamplified performances where singers can sing in tune without technological help, sometimes well into their 60s and beyond. They can do this because they don't stop singing. Many big superstars record their albums, which are then put into tune mechanically, and then go on tour where they often lip sinc (or mime as we used to call it) to a prerecorded vocal. They don't record their songs over and over again to get them perfect, and they don't need to rehearse (except perhaps their dance moves) for 'live' performances. The result is they are not using their singing voice: a young voice is fine without much practice, but as you get older, you need to exercise your singing voice, the vocal chords being a muscle. It really is a case of use it or lose it.
Singers such Ella Fitzgerald, Aretha Franklin and Dusty Springfield all retained their singing voices until older years; using modern techniques of recording and 'live' performance, their voices would probably have been seriously diminished by the time they reached their fifties, but as we know that did not happen.
'Live' performances are often mimed, particularly when energetic dancing is involved: it is impossible to sing accurately while doing the moves that Beyoncé, Britney or Madonna do. Try singing an entire song faultlessly for 4 minutes while going for a jog and you'll see what I mean: it simply cannot be done. The perils of miming were highlighted in 1989 when Milli Vanilli's backing track stuck during a 'live' performance, but that was not the exception that everyone seemed to assume. I don't know how people can sleep when they charge fans a fortune for a mimed performance. It's worse than pub karaoke, where at least you know that the vocal, even if it's dodgy, is real.
To me, miming is like cheating at cards and autotune is the musical equivalent of performance-enhancing drugs in sport. Here is an item broadcast 2 years ago on RT on the issue; it told me that the fraud being foisted upon music lovers is even worse than I had previously supposed.