Originally posted by Caliban
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Your link will "reduce" everything to CD quality - 44.1 kHz sampling at 16 bits. Some people claim that higher sampling frequencies and more bits are better. It is certainly the case that for producing the CDs there are a lot of advantages in using higher sampling rates and more bits per sample, or other techniques such as DSD. However, for the final produced article many engineers and mathematicians would argue that 44.1 kHz at 16 bits is good enough. Most humans can't hear above 20 kHz, so 44.1 kHz sampling should be enough.
Some equipment may work better with higher sample rates, or more bits, or may simply be better made. It's very difficult to tell IMO.
My personal hunch is that having a few more than 16 bits may give improved sound quality - it will reduce the noise floor, and in turn that may increase the apparent loudness of the sound.
Oddly that is where mp3 and similar systems may do slightly better than 16 bit PCM, as it's quite easily possible to enocde masters at 20 bits or 24 bits using these compression forms. However, most lossy compression algorithms introduce significant artefacts/noise, which would tend to have the opposite effect on perceived audio quality. You may remember the R3 DAB bit rate debacle from quite a few years ago, when the DAB bit rate was reduced to 160 kbps. Many people complained, and said it was clearly inferior to the 192 kbps streams. DAB was designed to work at 256 kbps, but by reducing the bit rate broadcasters can fit more stations on to the same transmission system. DAB uses a codec called mp2, which in terms of audio quality is considered less good than mp3. For example we might establish a rough equivalence of 160 kbps DAB (mp2) with 128 kbps mp3, and 256 kbps DAB (mp2) with 192 kbps mp3. AAC is considered to sound better than either of these for a given bit (data) rate. This means it actually discards more data than other codecs, but it only attempts to discard data corresponding to sound which we probably wouldn't hear anyway. At 256 kbps and above, most lossy codecs should sound more or less indistinguishable to most people, but at lower bit rates there are clear differences, and noticeable quality loss.
I am more sceptical about the use of higher sampling rates.
At very low bit rates, quality suffers a lot, and lossy codecs might only be considered suitable for speech, or very limited (comparable to AM radio perhaps) audio, and stereo isn't great either. One of the problems is a loss of high frequencies, which really dulls the sound. However, quite a few years ago, a system called SBR (Spectral Band Replication) was developed, which "regenerates" the missing high frequencies to give a more acceptable result. It doesn't actually regenerate them - it's a fake process, but fools the ear into thinking that the sound is closer to what the original might have been. This has been developed into AAC-HE which can give passable results for many not too critical listeners.
This way the broadcasters can send out more channels without using up all the spectrum they have available. There are other trade offs possible. For example, rather than trying to send out two very high quality channels, they could perhaps transmit 5 or more somewhat lower quality channels for surround sound systems using the same overall data rates. It is possible that many users would prefer that - if they had appropriate playback equipment.
If you are happy with your system as it is, then don't worry too much about it. The Airport express link should be capable of delivering much higher quality (CD quality) than the streamed audio from the BBC. However, you should try to pick up the best of the R3 streams - which others seem to have now confirmed is a 320 kbps compressed stream. If you find you are picking up a lower bit rate stream you might notice the lower quality.
One other thing - it would not be worth spending a lot more for studio master downloads at (say) 24/192, as with your link these would be transformed down to 16/44.1 - though if you ever got equipment which could play 24/192 you might then get a benefit. If you are always going to use that link, then don't even try to improve quality by buying any so-called hi-res files - they may sound OK, but shouldn't be any better than regular CD quality. That should answer your last point.
Despite all this, do remember that perceived audio quality isn't always determined by bit rates and all this technical stuff. A relatively poor technical system may be capable of giving very musical results on some material (may depend on the instruments and music), and in contrast, no matter how good technically the transmission system is, if the basic recording is **** then the replay will also be ****.
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