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Difficult material, Harder to encode
davexnet
post Feb 23 2011, 19:53
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I noticed it on my TV. The cable company encodes the audio in a lower bitrate on the SD channel compared to the HD version.
On most material it's not objectionable, but on old movies, such as those on TCM, the SD version often sounds like crap,
while switching to the HD version there's a massive improvement.

Trying to encode material such as the 4 Seasons early music (Ragdoll, etc) is difficult. The original sounds
pretty rough to begin with (don't know what happened to their master tapes) and the encoded mp3
sounds soft. It really doesn't capture the edginess of the uncompressed file

Dropping back to 3.97 of Lame (compared to 3.98.4) seems like a "harder" sound, and at first glance
sounds like it captures this difficult material more faithfully, but listening to it for a while
it just sounds ugly.

I made this comparison using 3.97 in Razorlame and 3.98.4 in LamedropXP (set to quality = 100)
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pdq
post Feb 23 2011, 21:42
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QUOTE (davexnet @ Feb 23 2011, 14:53) *
I noticed it on my TV. The cable company encodes the audio in a lower bitrate on the SD channel compared to the HD version.

I would have guessed that the difference in bitrate was mainly due to stereo vs. surround sound.
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mixminus1
post Feb 23 2011, 21:51
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...and to address your second assertion - that of LAME "softening" the sound - have you done ABX tests to confirm this, or is this just what you've perceived from playing the tracks back to back?


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davexnet
post Feb 24 2011, 01:15
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I'm talking about old black and white movies on TCM from the 1930's and 40's.
Have these movies such a sound track? Whether it's that or just higher bitrate stereo, the sound is clearly better.
(and I'm only listening on a 2-channel stereo system). I don't have a way to sample the stream ditrectly,
but I'm guessing that the SD sound either has a lower bitrate or sample rate, or both.

Regarding the comments I made about the mp3 sound. When I first heard the default of lamedropXP (I only downloaded it yesterday)
it sounded very soft compared to the mp3 I got using Razorlame and some manual settings (vbr, 128-320, q=2).
I realize Razorlame is old and it doesn't seem to work properly with the recent Lame encoder, nor does it provide
all the proper switches.

I'm wondering if the issue I'm noting is really due to the difficult material. AS I mentioned, the old 4 seasons songs,
which don't sound that good to begin with.
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mixminus1
post Feb 24 2011, 02:08
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QUOTE (davexnet @ Feb 23 2011, 16:15) *
I'm wondering if the issue I'm noting is really due to the difficult material.

No need to "wonder" - just do an ABX test.

If you fail the test, it's just your perception; if you get a positive result, then you've got something and it would warrant further investigation.


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davexnet
post Feb 24 2011, 02:29
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QUOTE (mixminus1 @ Feb 23 2011, 17:08) *
QUOTE (davexnet @ Feb 23 2011, 16:15) *
I'm wondering if the issue I'm noting is really due to the difficult material.

No need to "wonder" - just do an ABX test.

If you fail the test, it's just your perception; if you get a positive result, then you've got something and it would warrant further investigation.


OK. I'll see if I can set something up I can do myself.
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Destroid
post Feb 24 2011, 08:22
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I think in addition to still doing ABX testing, you should prepare to notice that older recordings actually compress worse (meaning higher bitrate). Distortions in the forms like tape-hiss/pop/rumble are completely random and audible ones (especially in the lower-dB 'quieter' recordings) distortions are preserved, which ends up accumulating more bits when using VBR in audio. I'm sure several persons can testify this is also true when encoding video from film sources, as the film grain (distortion) is not discriminated and ends up being preserved at the price of higher bitrate compared to digital video sources. Of course this is just in general, there are always a few exceptions.


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