26 Oct
2011
26 Oct
'11
4:51 p.m.
On Mon, Oct 24, 2011 at 10:33 PM, Paul Davis <paul(a)linuxaudiosystems.com> wrote:
Al, I have a huge amount of respect for your technical
knowledge but
offhand remarks like this require some countering in an online forum.
Its true that low bit rate psycho-acoustic lossy compression does
remove some "good" information. But my impression is that at
"appropriate" bit rates, an overwhelming majority of humans cannot
differentiate between an mp3 and the original recorded audio. I'm not
entirely clear what "appropriate" means, but I believe that its hard
for most people to differentiate (in a double blind test) at 128kbps,
very hard at 192kbps and essentially impossible at rates above
256kbps. Should I update my understanding of this?
Ill take issue with that slightly. Namely that if you want to be that
technical, you have to explicitly state the conditions of the test.
Listening conditions probably make the largest difference to someone's
ability to discern the difference between a lossy compressed file and
the original. With good listening conditions, including a relatively
quiet environment and an even halfway decent pair of passive isolation
headphones, you will likely hear some difference if you are looking
for it. Then you get into how much someone would notice, but I
suspect until you get to 256 most people under such conditions(Which
are not even ideal) would be able to hear if they are listening for
it.
Note that it is hard for me to judge this as I would wager a fair
guess my ears are much better trained(As I would imagine most on this
list falls into this as well) than what would be considered the
'average' listener, so some assumptions I make are just that, while I
can keep in mind this fact it means I am not a particularly good judge
at times of what others will or won't hear. Then again I work under
the rule of 'a sound system is only as good as the sum of its weakest
components' and as a result will do everything as good quality as I
can in most cases assuming that even if people don't realize there is
a difference consciously, they might subconsciously.
If they are not listening for it however, aka casual listening, then
we are in a different realm entirely. I still suspect that for many
enthusiasts at least 192 would be the minimum for MP3s, with 128 being
the minimum for more efficient codecs(ie. AAC and Vorbis), likely why
those numbers can be found in the various online music stores that are
popular today, at least in a semi decent listening environment.
Now you get to an actual good listening environment, and especially
with enthusiasts in such, and your requirements will likely increase.
Seablade