I picked up a copy of "The Great Fantasy Adventure Album" (I
think it's put out by Telarc?), which has a LOT of very low-frequency
bass content. When I encode it to AAC, even at a relatively high
bitrate, like 192 or 224 kbps, it seems like a good portion of the low
bass content is being lost.
I know that compression algorithms like MP3 and AAC work by
removing content that the algorithm determines to be less audible than
the rest of the signal, but do they also have an arbitrary low-end
attenuation?
Usually, I can't tell the difference between a CD and a 224
kbps AAC file of the same song, but it's noticeable with this one
bass-heavy example.

Scott Gardner

Scott Gardner a écrit :
I picked up a copy of "The Great Fantasy Adventure Album" (I
think it's put out by Telarc?), which has a LOT of very low-frequency
bass content. When I encode it to AAC, even at a relatively high
bitrate, like 192 or 224 kbps, it seems like a good portion of the low
bass content is being lost.
I know that compression algorithms like MP3 and AAC work by
removing content that the algorithm determines to be less audible than
the rest of the signal, but do they also have an arbitrary low-end
attenuation?
Usually, I can't tell the difference between a CD and a 224
kbps AAC file of the same song, but it's noticeable with this one
bass-heavy example.

Scott Gardner


You can check that in SoundForge.
You can compare the original .wav with the compressed AAC or MP3.
Starting from this point you can make the necessary adjustement in
low-pass filter (depends on your compression software). I don't know AAC.

I picked up a copy of "The Great Fantasy Adventure Album" (I
think it's put out by Telarc?), which has a LOT of very low-frequency
bass content. When I encode it to AAC, even at a relatively high
bitrate, like 192 or 224 kbps, it seems like a good portion of the low
bass content is being lost.
I know that compression algorithms like MP3 and AAC work by
removing content that the algorithm determines to be less audible than
the rest of the signal, but do they also have an arbitrary low-end
attenuation?

Not that I know of. Low-pass filtering is usually employed (good encoders
allow you to adjust the cutoff) because it's less efficient to encode high
frequencies than low frequencies (related to log f).

Usually, I can't tell the difference between a CD and a 224
kbps AAC file of the same song, but it's noticeable with this one
bass-heavy example.

What are you using for an encoder?

On Sun, 21 Dec 2003 10:40:11 -0500, "Mark Zarella"
wrote:

I picked up a copy of "The Great Fantasy Adventure Album" (I
think it's put out by Telarc?), which has a LOT of very low-frequency
bass content. When I encode it to AAC, even at a relatively high
bitrate, like 192 or 224 kbps, it seems like a good portion of the low
bass content is being lost.
I know that compression algorithms like MP3 and AAC work by
removing content that the algorithm determines to be less audible than
the rest of the signal, but do they also have an arbitrary low-end
attenuation?

Not that I know of. Low-pass filtering is usually employed (good encoders
allow you to adjust the cutoff) because it's less efficient to encode high
frequencies than low frequencies (related to log f).

Usually, I can't tell the difference between a CD and a 224
kbps AAC file of the same song, but it's noticeable with this one
bass-heavy example.

What are you using for an encoder?

I'm using the AAC encoder in iTunes, so that may well be the problem.
It's not adjustable except for bitrate and sample rate.

Scott Gardner

In article ,
(Scott Gardner) wrote:


I'm using the AAC encoder in iTunes, so that may well be the problem.
It's not adjustable except for bitrate and sample rate.

Scott Gardner


i'm using an old copy of Soundjam.. which if i'm not mistaken kinda
turned into iTunes.

there's an option to highpass all encodings at 20hz. maybe you can't
turn it off?

--
cyrus

*coughcasaucedoprodigynetcough*

In article ,
(Scott Gardner) wrote:

I picked up a copy of "The Great Fantasy Adventure Album" (I
think it's put out by Telarc?), which has a LOT of very low-frequency
bass content. When I encode it to AAC, even at a relatively high
bitrate, like 192 or 224 kbps, it seems like a good portion of the low
bass content is being lost.
I know that compression algorithms like MP3 and AAC work by
removing content that the algorithm determines to be less audible than
the rest of the signal, but do they also have an arbitrary low-end
attenuation?
Usually, I can't tell the difference between a CD and a 224
kbps AAC file of the same song, but it's noticeable with this one
bass-heavy example.

Scott Gardner


iTunes has a switchable sub-10Hz filter in the MP3 prefs. Its outdated
encoder tends to make a mess down there. It's a common MP3 problem.

I haven't played with AAC enough to know how it handles bass. The real
test is to play back a song on my car stereo. Any disruption changes
the point where the speakers clip. My experience with the iTunes MP3
encoder is that it exaggerates bits of low frequencies in odd ways.

Now that I think about it, AAC is a Dolby technology, right? I can't
say that I'm a fan of Dolby.