VBR - What does 'quality' slider bar do?

[Ghosthunter]

I am using DMC to rip to MP3s in Variable Bit Rate with a low of 192k and a high of 256k. I get that. However, what does the 'Quality' slider bar do beyond that. And where should I set it. I currently have it set 3 notches away from the highest setting. There is no discussion of what this does in the help menus other than it 'sets the quality.'

Thanks,
Joe

[xoas]

Re: VBR - What does 'quality' slider bar do?

Roughly speaking, a quality setting in Lame (or other codecs that use quality settings) refers to a variable bitrate range. Higher quality settings reflect higher bitrates and lower settings reflect lower settings.

As I understand it, a quality setting differs from a variable bitrate setting in that the upper and lower bitrate points are not firmly fixed. Rather they are adjusted with the idea being to preserve a certain level of recording quality while recognizing that the bitrate range needed to maintain a given level of audio quality will vary from one track to the next.

Say you have one track that is a vocal solo and another that is a string quartet. These will differ in the amount of audio information they contain that needs to be preserved. If you use the same set variable bitrate on both, you run the chance that the 2 tracks will be of different quality relative to each other. Apart from any aesthetic considerations this result would also indicate that you are using extra disk space for the vocal solo or that you are losing more audio information on the string quartet or both. The use of quality settings results in a kind of variable variable bit rate that standardizes the amount of audio information preserved in each file relative to the audio information in the source.

Generally, this is an advantage but there may be situations in which either the use of constant bit-rate settings or a fixed variable bitrate setting will work better than a quality setting (primarily if your player has difficulty with wider variations in bitrates).

Hopes this helps.
If there is any inaccuracy in this explanation, feel free to clarify.

Best wishes,
Bill

[xoas]

Re: VBR - What does 'quality' slider bar do?

For the full scoop on the varous quality settings for mp3 see this:

http://wiki.hydrogenaudio.org/index.php?title=LAME#Hey.21_What_happened_to_.22--alt-preset.22.3F

(handy link provided by Wayne).

Best wishes,
Bill