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View Full Version : Is there a minimum bitrate Slimp3 will play?



Chet Wood
2004-04-09, 20:16
Someone gave me a CDR with MP3 files recorded at a bit rate of 32kbps.
They play fine under iTunes (quality's not fantastic, but the voice is
understandable.)

But when I try to play them on my Slim, there's just a click and a pop
at the beginning, then silence. The display shows the time counting
down as if it were playing.

Slimp3 specs state a max bitrate of 320kbps if memory serves, but I
couldn't find a minimum spec.

Or what else could be going wrong? (All my 192kbps music plays fine on
the slim.)

thanks

chet

seanadams
2004-04-12, 08:00
All mp3 bit rates are supported by both products, but SLIMP3 supports
only 44.1KHz (CD) and 48KHz (DAT) sample rates. 32KHz output will not
work on SLIMP3 due to a limitation of the DAC, but it does work fine in
Squeezebox (analog output only). 32KHz is not supported at all for
S/PDIF. That's not a limitation of the Squeezebox but a limitation of
s/pdif.

If you have any 32KHz files (these are generally quite rare), your best
bet it to decompress, resample to 44.1, and re-compress to mp3. Or if
you have the original source you can resample to 44.1 and then
compress, which will give you the best quality for a given bitrate. If
the original source is 44.1, just compress is directly - there is no
quality/compression advantage to down-sampling from 44.1 to 32KHz
before compression.

On Apr 9, 2004, at 8:16 PM, Chet Wood wrote:

> Someone gave me a CDR with MP3 files recorded at a bit rate of 32kbps.
> They play fine under iTunes (quality's not fantastic, but the voice is
> understandable.)
>
> But when I try to play them on my Slim, there's just a click and a pop
> at the beginning, then silence. The display shows the time counting
> down as if it were playing.
>
> Slimp3 specs state a max bitrate of 320kbps if memory serves, but I
> couldn't find a minimum spec.
>
> Or what else could be going wrong? (All my 192kbps music plays fine on
> the slim.)
>
> thanks
>
> chet
>
>

Derek Adair
2004-04-12, 08:13
On Mon, 12 Apr 2004, Sean Adams wrote:

> If you have any 32KHz files (these are generally quite rare), your best
> bet it to decompress, resample to 44.1, and re-compress to mp3. Or if
> you have the original source you can resample to 44.1 and then
> compress, which will give you the best quality for a given bitrate. If
> the original source is 44.1, just compress is directly - there is no
> quality/compression advantage to down-sampling from 44.1 to 32KHz
> before compression.

I have a SLIMP3. I have a number of radio shows and audio books that have
been sampled at a variety of different rates. Is there any method to
convert these on the fly? Alternatively, does anyone know of a script or
program to do a batch conversion? Does the last sentence there mean if I
keep the bitrate the same, the files will remain approximately the same
size?

Thanks,
Derek Adair
dadair (AT) iglou (DOT) com

seanadams
2004-04-12, 08:28
There are two different terms being used here, bitrate and sample rate.

Sample rate is expressed in KHz and it almost always 44.1KHz, but
sometimes 48KHz or 32KHz. This is the number of audio samples taken per
second when the sound is recorded from its analog source. 44.1KHz is
the sample rate used for CDs. 48KHz is used for DAT. 32KHz is used in
some low-fidelity voice recordings and radio sources. For uncompressed
audio, higher smaple rate == larger files. For mp3 compressed audio,
the sample rate is not so important - you generally want to use the
same sample rate as the original source, except in the case of 32KHz
where you might want to up-sample to get better compatibility.

The other term is "bit rate", and is expressed in kbps. The bit rate
is mostly what determines the sound quality, and can be anywhere from
32 to 320Kbps for mp3. Higher bit rate == higher quality == larger
files. The bit rate is chosen at the time the file is compressed from
WAV/AIFF into mp3.

A table might help to show which mp3 formats are supported:


Sample Bit Slimp3 Squeezebox Squeezebox
rate rate analog out digital out
(KHz) (Kbps)

32 32..320 No Yes No
44.1 32..320 Yes Yes Yes
48 32..320 Yes Yes Yes



Because of the way mp3 compression works, it is never advisable to
down-sample the source from 44.1 to 32KHz before compressing. It is
better to leave it at the original sample rate and let the mp3
compression algorithms do their work.


On Apr 12, 2004, at 8:13 AM, Derek Adair wrote:

> On Mon, 12 Apr 2004, Sean Adams wrote:
>
>> If you have any 32KHz files (these are generally quite rare), your
>> best
>> bet it to decompress, resample to 44.1, and re-compress to mp3. Or if
>> you have the original source you can resample to 44.1 and then
>> compress, which will give you the best quality for a given bitrate. If
>> the original source is 44.1, just compress is directly - there is no
>> quality/compression advantage to down-sampling from 44.1 to 32KHz
>> before compression.
>
> I have a SLIMP3. I have a number of radio shows and audio books that
> have
> been sampled at a variety of different rates. Is there any method to
> convert these on the fly? Alternatively, does anyone know of a script
> or
> program to do a batch conversion? Does the last sentence there mean if
> I
> keep the bitrate the same, the files will remain approximately the same
> size?
>
> Thanks,
> Derek Adair
> dadair (AT) iglou (DOT) com
>

Derek Adair
2004-04-12, 08:42
Sean,

I understand the difference between the two, although the grid at the end
is quite informative. Yes, the bitrates of the radio shows, etc. I'm
playing are all over the shop, but the sample rates aren't standard
either. I know there are some 32KHz mp3's in there, and I thought a few
16KHz ones as well (although I'm not at my server, so I can't verify
this).

My question still stands - is there any way to resample these on the fly,
or does anyone know of a tool to convert these en masse?

Thanks,
Derek


On Mon, 12 Apr 2004, Sean Adams wrote:

>
>
> There are two different terms being used here, bitrate and sample rate.
>
> Sample rate is expressed in KHz and it almost always 44.1KHz, but
> sometimes 48KHz or 32KHz. This is the number of audio samples taken per
> second when the sound is recorded from its analog source. 44.1KHz is
> the sample rate used for CDs. 48KHz is used for DAT. 32KHz is used in
> some low-fidelity voice recordings and radio sources. For uncompressed
> audio, higher smaple rate == larger files. For mp3 compressed audio,
> the sample rate is not so important - you generally want to use the
> same sample rate as the original source, except in the case of 32KHz
> where you might want to up-sample to get better compatibility.
>
> The other term is "bit rate", and is expressed in kbps. The bit rate
> is mostly what determines the sound quality, and can be anywhere from
> 32 to 320Kbps for mp3. Higher bit rate == higher quality == larger
> files. The bit rate is chosen at the time the file is compressed from
> WAV/AIFF into mp3.
>
> A table might help to show which mp3 formats are supported:
>
>
> Sample Bit Slimp3 Squeezebox Squeezebox
> rate rate analog out digital out
> (KHz) (Kbps)
>
> 32 32..320 No Yes No
> 44.1 32..320 Yes Yes Yes
> 48 32..320 Yes Yes Yes
>
>
>
> Because of the way mp3 compression works, it is never advisable to
> down-sample the source from 44.1 to 32KHz before compressing. It is
> better to leave it at the original sample rate and let the mp3
> compression algorithms do their work.
>
>
> On Apr 12, 2004, at 8:13 AM, Derek Adair wrote:
>
> > On Mon, 12 Apr 2004, Sean Adams wrote:
> >
> >> If you have any 32KHz files (these are generally quite rare), your
> >> best
> >> bet it to decompress, resample to 44.1, and re-compress to mp3. Or if
> >> you have the original source you can resample to 44.1 and then
> >> compress, which will give you the best quality for a given bitrate. If
> >> the original source is 44.1, just compress is directly - there is no
> >> quality/compression advantage to down-sampling from 44.1 to 32KHz
> >> before compression.
> >
> > I have a SLIMP3. I have a number of radio shows and audio books that
> > have
> > been sampled at a variety of different rates. Is there any method to
> > convert these on the fly? Alternatively, does anyone know of a script
> > or
> > program to do a batch conversion? Does the last sentence there mean if
> > I
> > keep the bitrate the same, the files will remain approximately the same
> > size?
> >
> > Thanks,
> > Derek Adair
> > dadair (AT) iglou (DOT) com
> >

Tim Limon
2004-04-13, 07:29
> My question still stands - is there any way to resample these on the fly,
> or does anyone know of a tool to convert these en masse?
>
> Thanks,
> Derek
>
You can use CDex http://www.cdex.n3.net/ if your on a windows box. It has
the ability to resample.

--tim