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Good Bit Rate When Converting Tivo Audio to MP3?

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Anonymous
February 24, 2005 5:11:29 PM

Archived from groups: alt.video.ptv.tivo (More info?)

I like to save musical performances from television shows that I've
recorded with my Tivo. Without "Tivo To Go," I would just attach the
analog stereo outputs of the Tivo to my computer's sound card.

When encoding the MP3, what would be a sensible maximum bit rate? By
"sensible," I mean a bit rate that wouldn't exceed the effective bit
rate that Tivo uses itself when compressing audio.

For example, if Tivo's audio compression was similar to, say, a fixed
bit rate of 128 kilobits per second, there wouldn't be much point in
encoding an MP3 version of the output at 192 kilobits per second.
Anonymous
February 25, 2005 4:32:52 AM

Archived from groups: alt.video.ptv.tivo (More info?)

in article 1109283089.676571.298370@l41g2000cwc.googlegroups.com, C.T.K. at
ctkads@yahoo.com wrote on 2/24/05 2:11 PM:

> I like to save musical performances from television shows that I've
> recorded with my Tivo. Without "Tivo To Go," I would just attach the
> analog stereo outputs of the Tivo to my computer's sound card.
>
> When encoding the MP3, what would be a sensible maximum bit rate? By
> "sensible," I mean a bit rate that wouldn't exceed the effective bit
> rate that Tivo uses itself when compressing audio.
>
> For example, if Tivo's audio compression was similar to, say, a fixed
> bit rate of 128 kilobits per second, there wouldn't be much point in
> encoding an MP3 version of the output at 192 kilobits per second.
>

Actually, there's not much point in up-converting an encoding from one
bitrate to another.

In this case, that's not what you're doing. You're taking the digital audio
from the TiVo (bitrate irrelevant) and converting it to analog. You're then
going to record it digitally.

As with any analog to digital recording, you're going to get better results
with higher resolution and lower lossy compression.

So in fact, a 16bit 44.1 stereo recording with no lossy compression will be
of better quality than anything less.

Whether you hear a difference depends on many things....the type of audio,
the quality of your gear, your hearing ability, and knowledge of what to
listen for.

The best bet is to simply make a few recordings and encode them at various
bitrates. Play them back on the equipment you'll be using and determine if
you can hear a difference.

Keep in mind thought that while you may not be able to hear a difference on
the equipment you have now, you might some day and the only way to improve
the bitrate will be to re-record from the original source.

Your equipment is going to get better and many people learn to hear the
difference between low and higher quality encodings. On the other hand,
hard drives become bigger and cheaper very rapidly. What a shame it would
be in the future to have a bunch of recordings that aren't what they could
be, but know that they only take up a microscopic amount of your drive
capacity. Hence my advice to always encode at a higher quality than you
think you should...and then, higher than that;)

A footnote to all of this is that lossy compression does alter the sound of
the audio in a way that when you do re-encode, you do end up with a sum that
is *less* than the parts. IOW going from a CD to a 192kbps AAC file will
reduce quality quite a bit. Taking that new AAC file and converting it to
192kbps MP3 will reduce the quality more than simply having gone from CD to
192kbps MP3, but not nearly the same level as "twice the gap" between CD and
192kbps MP3.

My entire library of ripped CDs is encoded at 192kbps AAC, when I use TiVo
to play my iTunes library, the TiVo Desktop software will convert to MP3.
Fortunately the quality is really good to begin with and it uses a real-time
LAME encoder that does a really good job of preserving quality during the
conversion. The result is that my TiVo plays my AAC iTunes library at a
quality that nobody yet has suspected wasn't coming from my CD player.
Anonymous
February 25, 2005 5:49:26 PM

Archived from groups: alt.video.ptv.tivo (More info?)

On Thu, 24 Feb 2005 at 22:11 GMT, <ctkads@yahoo.com> wrote:

> When encoding the MP3, what would be a sensible maximum bit rate? By

A VBR setting using a good encoder like LAME will make that decision
for you, frame by frame.



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Anonymous
March 1, 2005 2:38:17 AM

Archived from groups: alt.video.ptv.tivo (More info?)

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Hash: SHA1

In article <1109283089.676571.298370@l41g2000cwc.googlegroups.com>,
C.T.K. <ctkads@yahoo.com> wrote:
>I like to save musical performances from television shows that I've
>recorded with my Tivo. Without "Tivo To Go," I would just attach the
>analog stereo outputs of the Tivo to my computer's sound card.
>
>When encoding the MP3, what would be a sensible maximum bit rate?

Why bother reencoding the audio? Your TiVo records audio in MPEG Layer II
format, which is a subset of the Layer III format commonly known as MP3.
Demux the program stream and use a lossless editor (such as WBIAS) to snip
out the bits of audio you want. Change the extension of the saved file to
..mp2 and you're done. The resulting file should play on anything that
handles MP3s.

TiVo audio is sampled at 32 kHz and encoded at 192 kbps. The sample rate is
a bit on the low side, but it's more than likely sufficient for TV audio
(which would be why they went with it).

_/_
/ v \ Scott Alfter (remove the obvious to send mail)
(IIGS( http://alfter.us/ Top-posting!
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