"RCE" wrote in message
...
"thunder" wrote in message
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On Mon, 13 Mar 2006 16:50:28 -0500, RCE wrote:
Nice job and good information. I admit I haven't followed the
progression
of mp3 technology based on the early low sampling rates that were used
and
the resultant losses. I was unaware that sampling rates of 256kbps were
even possible. Maybe there's hope. I wonder, for the Ipod fans, what
the
file size becomes if sampled at these higher rates.
Uncompressed CDs have a bit rate of 1411.2 kbps. So, a 256kbps sampling
rate will give a compression ration of @ 6:1.
Last I knew (probably outdated) the mp3 "standard compression" was like
12:1, and the sampling rate was around 88kbsp. Has this changed?
I believe the "default" sampling rate, to the extent one exists, is 128 kbs.
Since I don't download songs I'm not 100% sure, but I believe this is the
typical compression rate you might find for a song downloaded from one of
the retailers that offer such things. In my earlier eperiences with MP3
files, this is the rate that I encoded songs that I ripped form my CDs. I
did so because it was the default setting of the software I used and didn't
know any better. I can certainly tell the difference between the source
material and MP3 files encoded at this rate. And you really don't need high
end gear to tell the difference, at least I don't. Using my MP3 player and
a decent set of Sony full-sized studio cans, I can easily hear the
difference between a 128 kps MP3 and a FLAC encoding, or even an MP3 encoded
at a higher sampling rate.
After doing some research on the subject, I quickly changed my default
encoding parameters. All of the discussion on this forum heretofore has
been about using various levels of sampling at a constant but rate (CBR).
Just to confuse things further, as it turns out, MP3's don't have to be
sampled at a CBR. They can be sampled at a variable bit rate (VBR).
Obviously a piece music is anything but constant in its levels of complexity
throughout its length. It turns out that some parts of a piece of music
might sound just fine at a relatively low sampling rate while others demand
a much higher sampling rate to achieve the same level of perceived quality.
This is precisely what VBR encoding is designed to recognize and accomodate.
Theoretically, it should yield the optimal balance between the yin and yang
of file compression and sonic quality for a given level of overall sonic
quality desired, and the encoding demands required of the specific music at
hand.
To complicate things further, there is more than one MP3 encoder out there.
Fraunhofer and LAME are a couple of the more popular ones. I currently use
the LAME encoder and use a the VBR preset standard setting. Here is a short
description of LAME VBR preset settings:
________________________
Built-in presets
Lame features some built-in presets. Those presets are designed to provide
the highest possible quality.
They have for the most part been subject to and tuned via rigorous listening
tests to verify and achieve this objective. These are continually updated to
coincide with the latest developments that occur and as a result should
provide you with nearly the best quality currently possible from LAME.
If your goal is quality, these presets are highly recomended over any custom
set of parameters you might use. To activate presets, you should use:
lame --preset preset_name
VBR modes
--preset medium
This preset should provide near transparency to most people on most music.
The resulting bitrate should be in the 150-180kbps range, according to music
complexity.
--preset standard
This preset should generally be transparent to most people on most music and
is already quite high in quality.
The resulting bitrate should be in the 170-210kbps range, according to music
complexity.
--preset extreme
If you have extremely good hearing and similar equipment, this preset will
provide slightly higher quality than the "standard" mode.
The resulting bitrate should be in the 200-240kbps range, according to music
complexity.
____________________________
For a good understanding of MP3 encoding and the options available, go to
http://www.mp3dev.org/. There's more there than you really want to know.
Russ