I'm ripping and encoding with EAC and LAME 3.9.1, using alt-preset standard. But a lot of stuff, especially quiet vocal type music seem to be encoding at bitrates averaging between 128 and 160. Some older stuff (eg, CDs of old Doris Day or Bing Crosby recordings encode at almost a straight 128 (like almost all the frames are encoding at 128 - almost like I was using CBR). Now on some other stuff, I will see a large number of frames hitting 320, and rock and roll tends to come out at around 192. It really seems to be all over the map. So my questions is, is some of the stuff encoding at bitrates that low normal (it's freaking me out some), and if so, why are the bitrates that low, is it limited frequency range or limited dynamic range in the original or what?

Thanks all.

mono -> 128 kbit.

I have low volume music that stays around 160 kbit too.

First, check this thread of the recommended LAME compiles. It may provide some insight as to why different versions of LAME create MP3 files of different size/bitrate. BTW...the recommended compile that you should use is 3.90.3.

Then, check this thread for recommended LAME settings. It'll give an explanation of nominal bitrates and what can affect bitrates/filesizes of encoded files.

Old recordings such as the ones you mention usually were mono AND were very quiet.
The first two Beatles albums, for instance, were mono and I get an average of 127k on the first one and 145 on the second one.

Just trust -aps.

Thanks for replies, I'm reassured. I checked and I am using 3.90.3 in fact. Great forum!

@ahfairley,
With mono recordings you could even add -b 96 to your --alt-preset commandline (overriding the default 128 kbit/s lower limit) and get the same quality at lower bitrates (if bitrate matters to you). This was discussed here some time ago and agreed to be safe IIRC, I could not find the thread though.

Really? I thought the consensus was "not mess with the presets"
If there's no quality improvement I would leave it as it is.

Mono recordings usually, in my experience, end up around 125-140 kbps when using aps with lame. Mono recordings require only 1/2 the nominal bit rate, since it is just one channel of information to encode. I am probably saying it wrong, but hopefully you get the idea.

Well, 1/2 if both channels are not related to each other in any way in a normal stero file. It's a lot more then 1/2 in the real world though due to joint stero (I think that's what it's called).

Also, less high frequency content in older recordings can result in a lower bitrate. Maybe also the masking quality of noise in older recordings too? (not positive about that)

I've seen 144kbps with a modern day song (not a mono recording).
Actually I got low bitrates with every codec I tried to encode it with...

Bit rate of certain song in VBR mode depends on several things:

1. Psychoacoustic masking threshold (some music is hard to encode due to low masking power... music with rich harmonic structure for example)

2. Stereo separation - "monoish" signals are compressed to up to 50% of their size with M/S (Joint Stereo) algorithm. Signals with strong separation require much more bits

3. Impulse signals, like castanets, hihats, etc.. require "overcoding" in MP3 in order to eliminate pre-echo. Quiet passages require less bits.