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David & Renee MacDonald
2005-03-06, 15:17
I have backed up all my MP3 recordings onto an external hard drive. Does the
quality of the MP3s suffer from repeated copying like some image files
do(Jpeg)?

David



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Mitch Harding
2005-03-06, 15:32
If you are copying data from one digital source to another (ie
internal hard drive to external hard drive), there is no loss of
quality. This is true whether the file is an MP3, JPG, or anything
else. The copy is identical to the original.

Loss of quality only comes into plan on analog copies. It's
theoretically possible on digital copies if you've got bad hardware,
but in those cases it's rarely a silent data corruption -- usually
you'd see other problems as well.

Mitch
www.mitcharf.com


On Sun, 6 Mar 2005 17:17:41 -0500, David & Renee MacDonald
<davidmacdonald (AT) sympatico (DOT) ca> wrote:
> I have backed up all my MP3 recordings onto an external hard drive. Does the
> quality of the MP3s suffer from repeated copying like some image files
> do(Jpeg)?
>
> David
>
> --
> No virus found in this outgoing message.
> Checked by AVG Anti-Virus.
> Version: 7.0.308 / Virus Database: 266.6.2 - Release Date: 04/03/2005
>
>

Stephen Ryan
2005-03-06, 15:48
On Sun, 2005-03-06 at 17:17 -0500, David & Renee MacDonald wrote:
> I have backed up all my MP3 recordings onto an external hard drive. Does the
> quality of the MP3s suffer from repeated copying like some image files
> do(Jpeg)?
>
> David

Yes and no; MP3 and JPEG are both "lossy" compression schemes, which
means that the process of creating such a file throws away part of the
information in the original audio signal / image, generally because the
information is deemed to have minimal significance. Both schemes
typically have a tunable threshold, where the user may set the level of
detail which is deemed to be significant. In practice, that
significance level sets the balance between saving disk space and the
quality of the resulting file.

Once the file is created, though, it's the same as any other file, and
you may make as many backups of it as you like without affecting the
quality any further. Backups are bit-for-bit identical to the original
files (well, they're supposed to be, anyway; if they're not, you've got
BIG problems).

I think the advice you got pertains to editing files; typically, you
cannot edit a compressed file directly. You must first open it to the
uncompressed form, make the modifications, then re-save it. At this
point, the file has already lost some of the fine details due to the
original compression, and the process of saving it after making
modifications means that yet more detail will be lost. For this reason,
you generally don't want to modify JPEG or MP3 files after they've been
created unless you can't help it.

Jack Coates
2005-03-06, 15:53
David & Renee MacDonald wrote:
> I have backed up all my MP3 recordings onto an external hard drive. Does
> the quality of the MP3s suffer from repeated copying like some image
> files do(Jpeg)?
>
> David
>
>

If copying files, neither format will be changed at all.

If continually re-compressing the same file over and over again, quality
will suffer for both formats.

If deleting the files, quality will be reduced significantly.

Moral of this story is "don't do that".

--
Jack at Monkeynoodle dot Org: It's a Scientific Venture...
Riding the Emergency Third Rail Power Trip since 1996!

Phil Karn
2005-03-06, 19:04
Others have already pointed out that MP3 files are like any other kind
of computer file; as long as no errors occur during copying, the copies
will be exactly identical to the original. Only if you decompress and
recompress will there be any further degradation.

Having said that, let me make a plug for FLAC (Free Lossless Audio
Compression). Not only does FLAC not lose *any* quality from the
original PCM WAV format (the format on standard audio CDs) but the FLAC
header also includes a built-in MD5 hash of the uncompressed audio. This
lets you verify a FLAC file to ensure that it's not corrupted. (You use
the command "flac --test file.flac"). I don't know of any other commonly
used audio format with this *very* nice feature.

FLAC uses much more space than the lossy formats like MP3, Ogg Vorbis
and AAC, but modern disks are *so* roomy and cheap that this just isn't
a big deal anymore for a desktop machine.

I chose FLAC as my primary format on my Slimserver, and I can still
produce lossy compressed versions from the FLAC masters as needed for
various portable players.

Phil

Jeffrey Gordon
2005-03-06, 19:31
Patrick Dowling wrote:

> On average what level of compression are you seeing? I know there are
> many factors, but for space planning I'm looking for a general estimate.
>
> Pat
>
> On Mar 6, 2005, at 8:04 PM, Phil Karn wrote:
>
If you are lucky you may see 2:1 compression, however it is generally
less than that. However being able to get a 250GB harddisk for ~$100
why would the compression really matter ;)

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Bruce Hartley
2005-03-07, 01:30
As long as you do a file copy onto the other device there will be no
degredation.
This would also apply to JPGs.
You would only get degredation if you actually opened the JPG and saved it
again, which could possibly created compression artefacts.

Likewise if you re-encoded all your MP3s onto your backup drive, the quality
would reduce, but there is no need to do it.

Rgds,
Bruce.

"David & Renee MacDonald"
<davidmacdonald (AT) sympatico (DOT) ca> wrote in message
news:006101c5229a$50671cd0$6500a8c0 (AT) david (DOT) ..
>I have backed up all my MP3 recordings onto an external hard drive. Does
>the quality of the MP3s suffer from repeated copying like some image files
>do(Jpeg)?
>
> David
>
>
> --
> No virus found in this outgoing message.
> Checked by AVG Anti-Virus.
> Version: 7.0.308 / Virus Database: 266.6.2 - Release Date: 04/03/2005

Bruce Hartley
2005-03-07, 01:33
So are you saying that a FLAC album takes between 360 and 720 MB?

Rgds,
Bruce.

"Jeffrey Gordon" <jeff (AT) thetank (DOT) org> wrote in
message news:422BBD10.1070806 (AT) thetank (DOT) org...
>

John L Fjellstad
2005-03-07, 03:17
On Mon, Mar 07, 2005 at 08:33:32AM -0000, Bruce Hartley wrote:
> So are you saying that a FLAC album takes between 360 and 720 MB?

I seem to remember when I tested out FLAC vs MP3 sizes, the flac files
would be on average 3 times the size of the mp3 files (with the mp3
files compressed with --preset extreme in lame)

--
John L. Fjellstad
web: http://www.fjellstad.org/ Quis custodiet ipsos custodes

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Michael Peters
2005-03-07, 03:44
On Mon, 7 Mar 2005 02:17:46 -0800, John L Fjellstad
<john-slimlist (AT) fjellstad (DOT) org> wrote:
> On Mon, Mar 07, 2005 at 08:33:32AM -0000, Bruce Hartley wrote:
> > So are you saying that a FLAC album takes between 360 and 720 MB?

flac sizes for five albums -

1) Chagall Guevara - Chagall Guevara - 350.8 MB flac, 72 MB lame 192VBR
2) U2 - War - 278.3 MB flac, 53.6 MB lame 192VBR
3) Arlo Guthrie - Alice's Restaurant - 195.2 MB flac, 48.4 MB lame 192VBR
4) Cracker - Kerosene Hat - 429.9 MB flac, 99.0 MB lame 192VBR
5) Kimi Hayes Band - Red 14 - 350.9 MB flac, 61.7 MB lame 192VBR

Average ratio of flac to lame 192VBR - 4.8

That's with preset-standard (192 VBR), not preset-extreme.

--
http://mpeters.us/

Pat Farrell
2005-03-07, 10:29
Bruce Hartley wrote:

>So are you saying that a FLAC album takes between 360 and 720 MB?
>
>
Most of mine are much closer to 200mb.
FLAC compresses about 2 to 1 for me.
a CD can hold 720 or 800 mb, which would
compress to 360 or 400, but very very few
commercial CDs have anything like a full CD,
esp pop and country, etc.

Since FLAC is free and fairly fast and totally lossless,
why not just try it on some of your music.

--
Pat Farrell pfarrell (AT) pfarrell (DOT) com
http://www.pfarrell.com

Patrick Dowling
2005-03-07, 19:07
On average what level of compression are you seeing? I know there are
many factors, but for space planning I'm looking for a general
estimate.

Pat

On Mar 6, 2005, at 8:04 PM, Phil Karn wrote:

> Others have already pointed out that MP3 files are like any other kind
> of computer file; as long as no errors occur during copying, the
> copies will be exactly identical to the original. Only if you
> decompress and recompress will there be any further degradation.
>
> Having said that, let me make a plug for FLAC (Free Lossless Audio
> Compression). Not only does FLAC not lose *any* quality from the
> original PCM WAV format (the format on standard audio CDs) but the
> FLAC header also includes a built-in MD5 hash of the uncompressed
> audio. This lets you verify a FLAC file to ensure that it's not
> corrupted. (You use the command "flac --test file.flac"). I don't know
> of any other commonly used audio format with this *very* nice feature.
>
> FLAC uses much more space than the lossy formats like MP3, Ogg Vorbis
> and AAC, but modern disks are *so* roomy and cheap that this just
> isn't a big deal anymore for a desktop machine.
>
> I chose FLAC as my primary format on my Slimserver, and I can still
> produce lossy compressed versions from the FLAC masters as needed for
> various portable players.
>
> Phil
>

Phil Karn
2005-03-11, 18:43
Patrick Dowling wrote:
> On average what level of compression are you seeing? I know there are
> many factors, but for space planning I'm looking for a general estimate.

A very rough rule-of-thumb is about 50% (2:1). You get better than that
on quiet classical music, and worse on loud, volume-compressed rock.

Phil

Phil Karn
2005-03-11, 18:48
Here's another data point for comparison. I recently bought the
Magnatune label album "Nocturne" by "The West Exit" and was given my
choice of file format to download. Here are the sizes:

# 44k/16bit WAV: 507meg zip of perfect quality WAVs.
# FLAC: 357meg zip file of perfect quality FLAC files.
# OGG: 65meg zip file of high quality Ogg Vorbis files.
# 128kb MP3: 47meg zip file of 128kb MP3 files.
# MP3 VBR: 84meg zip of high quality MP3 VBR files.
# Mac iTunes: 58meg iTunes OSX AAC files.
# Mac MP3: 96meg OSX & OS9 compatible 256k MP3s.