low bitrate artifact?

2005-10-04 06:00:13

A relative ask me to put some things onto CD-R in mp3 format. Lots of content for use in the car. Part of this was a book, spoken audio, the rest was music albums of varied types.

I use the Lame preset fast standard for the music. Since I read that the Fraunhofer codec was better for low bitrates, I experimented a bit with the possibilities in the included facility of CoolEdit. First I converted to 22.05kHz mono, then I chose a fairly low bitrate VBR that sounded good to me -- without extensively agonizing over it. I mailed everything back to her. Today I got a written report.

The music "sounded great" but the story was "a bit strange." The " volume changed frequently" making it not so comfortable to listen to. I know that various things could be wrong, such as the acoustics of the automobile, a fault in the player with lower bitrates, or even just the dynamic range of the reader(s) voice, but my question is about the encoding. Things sounded fine to me, in my home environment, but is there some known low bitrate mp3 artifact that is experienced as abnormal level changes by some people?

low bitrate artifact?

Reply #1 – 2005-10-04 06:31:32

I think the benefit of FhG at lower bitrates is a thing of the past.  Lame has made great leaps in quality across the spectrum (not sure how low) since that original assessment.  Someone who is more experienced/knowledgeable than myself can verify/refute these comments...

low bitrate artifact?

Reply #2 – 2005-10-04 08:25:12

It may well be that Lame would work fine, but I think that is probably irrelevant to this.

low bitrate artifact?

Reply #3 – 2005-10-04 17:13:24

There were some encoders which could produce "drop-out" artifacts, seek for more info on ff123's page.

low bitrate artifact?

Reply #4 – 2005-10-04 19:41:13

Interesting but probably not the same thing. The description was of the "volume" going up and down. However, since I did not hear the problem, I'm not sure what may really be going on. I'm trying to get some more detailed feedback, but this person is frequently on the road for days at a time, so it may take a while.

low bitrate artifact?

Reply #5 – 2005-10-04 20:25:47

What kind of audio book is it ? I mean, does the sound sometimes com from the center and sometimes from left or right ? If so, the sound that comes from left or right will likely sound quieter in a mono-downmix.

Sebi

low bitrate artifact?

Reply #6 – 2005-10-05 03:59:43

I prepared it. I listened to it. I can and have listened again since receiving her feedback. I don't precieve the problem. That's why I ask "experienced as abnormal level changes by some people?" She found it so extreme as to be uncomfortable, I don't hear it at all. I suspect specualtion will get me nowhere. Maybe I will eventually get more information from her.

low bitrate artifact?

Reply #7 – 2005-10-05 07:05:24

I don't have any experience first-hand, but I've heard people say a couple of times that they could very easily hear artifacts in the car.

Maybe it's related to how the car audio component  upmixes the sound to more than two speakers?

low bitrate artifact?

Reply #8 – 2005-10-05 07:42:09

Have you considered the possibility that one of the speakers in her car is installed in the wrong phase. Inside a car this could easily have the effect of making voices sound like they are changing in volume, especially if you are moving your head around. It is also plausible that phase artifacts present in low-bitrate MP3s could exacerbate the situation.