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Better codecs: will they deliver quality or quantity?
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We've had endless debates on here about if/when mp2 rolls over and AAC
+ takes over, will the newer codec be used to deliver the same number
of higher quality services, a larger number of equivalent quality
service, or a few more slightly higher quality services, compared to
the situation with mp2.
I thought "the middle way" was most likely, but I came across a
counter example the other day. You've probably all seen this example
without thinking about it.
mp3 was designed to be used at 128kbps, and most encoders default to
this bitrate. It's not perceptually transparent at this bitrate - a
fair comparison might be that it sounds like a reasonable cassette
tape, which is normally what it's replacing in portable devices.
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I would say it sounds a lot better than tape. No matter how good the
reproduction of tape
you always had the hiss , even with noise reduction. Thats something
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True , but the artifacts will come and go depending on what the
current waveform is. The hiss on tape is always there, albeit
sometimes inaudible if you're listening to something loud.
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Remember many years ago listing to a tape done by the late Angus
McKenzie of a cassette replay system with Dolby A in use IIRC, and was
struck by the velvet silent background:)
Excellent audio quality.. a lot there didn't believe cassette could be
that capable!...
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Apparently Dolby A was very good, but with the electronics of the day it
was expensive to implement, so not much good for domestic systems. Hence
they invented Dolby B, which did pretty well with a lot less
electronics. (Dolby C came later to improve on Dolby B).
Richard E.
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I was lucky, I had Dolby C on my walkman.
You had to have the volume turned up fairly high, or be listening
somewhere fairly quiet, to hear hiss with that.
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With a 3 head Nakamichi deck, Dolby C and the right choice of Chrome
tape I could A-B switch between a CD and its off-tape recording a
fraction of a second later. I don't remember anyone who could reliably
spot any difference. Made me a bit disappointed with CD performance for
a while, I'd been brainwashed into thinking it was far superior to
tape..
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The problem I used to find with cassette tape was that recordings always
seemed to deteriorate with time. My old Dolby C cassette recordings
don't sound anywhere near as good today as they used to. The sound
becomes muffled, and to makes things worse that affects the Dolby
system, so the playback never seems to sound quite right.
Richard E.
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Plus hiss between tracks is vastly preferable to artefacts during
them!
(Not that I'd swap decent VBR mp3 for a cassette tape any day!)
Cheers,
David.
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Actually noises that come and go tend to be more annoying than constant
noises. This is why Dolby B and C were designed with sliding filters so
that the hiss at high frequencies didn't end up becoming modulated by
the level of sound in the lower frequencies. They referred to this as
noise modulation and they reckoned it could be a lot more annoying than
a constant hiss.
Richard E.
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The advantage of that is that you get sort of used to the constant hiss.
The artefacts change all the time so you keep hearing them.
Try a 128 kbps station with pop music. You can hear the coding of the
treble changing all the time depending on how difficult the current
frame is. It sounds like an old cassette tape with dropouts.
gr, hwh
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It's comparing apples with oranges. You get artefacts with128kbps mp3
that you'd never get with tape. You get hiss with tape that you'd
never get with mp3.
That said, with a decent walkman (I had a really nice slim clamshell
Panasonic back in the 1990s - great when it worked) the only place I'd
ever notice any background noise was between tracks when listening in
bed. Outside the house (which is where most walkmen are used) it was
inaudible and irrelevant. Dolby-C/azimuth mismatch were greater
problems, and comparable (in terms of annoyance) to the kind of issues
you might get with mp3 artefacts at 128kbps CBR a few years ago. Mind
you, it's a lot easier to use a higher bitrate than it ever was to
avoid the problems associated with cassette tapes!
Horrible walkmen, especially without Dolby, were just that: horrible.
There are equally horrible mp3 players, with easy audible noise - just
like bad on-board (especially laptop) sound cards.
The laws of physics allow perfectly good audio equipment, "easily"
meeting 120dB dynamic range. It's bad design that brings it down to
60-70dB in cheap-n-nasty equipment (whatever the specs say).
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you simply don't get
with digital systems other than the very low level hiss you get with
all electronic audio
devices (but nothing will get rid of that apart from a change in the
laws of physics).
Thats also one advantage DAB always has over analogue radio no matter
what codec is used.
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Very important with a walkman-style radio with a headphone cable
aerial! Irrelevant with a roof top aerial, given the dynamic range of
most stations (FM and DAB). Back to the original comparison, cassette,
even with Dolby-C, struggles to match the best that FM can do.
Cheers,
David.
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Microsoft invented Windows Media Audio in an attempt to improve on
mp3, with their own proprietary algorithm. They claim, somewhat
optimistically, that 64kbps WMA is equivalent quality to 128kbps mp3.
Sometimes they even claim that 64kbps WMA sounds better than 128kbps
mp3.
If you're ripping a CD with Windows Media Player, go into the settings
and click "tell me more", you can read all about it.
So given this amazing new codec, what settings does Windows Media
Player use by default? 128kbps WMA.
So by default, they don't take _any_ advantage of the advertised
increase in efficiency to fit more CDs onto your PC or portable audio
device. They use _all_ of this advantage to deliver higher sound
quality.
iTunes is another example, but this time using AAC. The default is
128kbps AAC.
Can we even begin to dream that broadcasters will be half as sensible?
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Given that they'll have long leases on 128kbps kilostreams, it's likely
that they'll fill them. On the other hand, for short hops an E1 link
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Ah, but with what? 1x128kbps or 2x64kbps? (or 3x40kbps + data?!)
What about new muxes, both here and abroad, starting form scratch?
Cheers,
David.
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(2Mbps) from a cableco is about the same price as a BT Kilostream.
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Although it is difficult to predict what broadcasters will do I tend to
think we will end up with rather a mixture of different bit rates and
levels of quality.
Looking at the range of DAB services already broadcasting there is some
range of bit rates. Firstly looking at the mono stations, some opt for
the minimum 64k, while others go as high as 96k. Looking at the stereo
station nearly all use 128k, but then there are now 4 London stations
using 160k, as well as 2 national stations.
I think that the high financial cost of broadcasting DAB has been a huge
factor in pushing bit rates down, but there is still some variation
around the low end.
When aac+ makes broadcasting cheaper, I would think that would mean less
pressure distorting quality levels towards the low end, leading to a
more sensible range of quality levels. Whether or not anybody goes as
high as 128k aac is a difficult question, but I would think we could
expect plenty of 64k aac+ services. Presumably some would go as low as
32k or even 24k, but then again at those rates they would take up such a
small proportion of the available capacity, that perhaps it wouldn't
matter much.
Another point perhaps is that if 32k was used, it would be rather hard
to find enough broadcasters to fill up a multiplex. So unless they fill
it up with mobile TV, then there should be enough capacity going spare
for some services at 64k or more.
Richard E.
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Cheers,
David.
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