LAME VBR Settings and the Y Switch

2018-03-30 14:53:34

Hello -

It has been years since I've posted to Hydrogenaudio - but I have some questions regarding the LAME MP3 encoder.  I am using the latest stable release - version 3.100.

I know that when you designate a VBR setting - that LAME uses  built in settings - and ignores any custom sttings, is this correct?

For example - if I were to use -V 2 - and set the Y switch - doesn't LAME ignore the Y switch and just encode with -V 2 and the built in options?  Or if I set a algorithm quality of 0 - doesn't LAME use whatever is set as default for this -V 2 setting?

My second question is - what happens if we use floating point numbers and try to use custom settings?  For example - if I wanted to use -V 2.5 - could I then change the algorithm quality and set the -Y switch - or does LAME still have its built in options for -V 2.5?

The reason I ask is because I wanted a little bit more bits by using 2.5 vbr setting - but still wanted to be able to set the Y switch.

Does this make any sense?  If not please let me know - thank you very much

Re: LAME VBR Settings and the Y Switch

Reply #1 – 2018-03-30 16:27:49

I doubt that there is any serious testing of quality taking place with anything other than standard -V settings, so why would you risk encoding using such an unknown setting?

Re: LAME VBR Settings and the Y Switch

Reply #2 – 2018-03-30 16:37:56

I don't think I'm going to try anything but the main settings - like -V 0, -V 1, -V 2, or - V 3.  What you said makes sense - I was honestly more just curious. 

I'm actually using -V 3 as I find the quality good but I know that the Y switch is turned on with this setting - so there isn't extra bloat trying to encode high frequencies (well where encoding the high frequencies would cause a bump in bitrate).

I was mostly just curious as I said.

Re: LAME VBR Settings and the Y Switch

Reply #3 – 2018-03-30 21:40:35

According to the wiki:
"The -Y switch can only be activated in VBR mode. By default, -V 3 to -V 9 use -Y. -V 0, -V 1, and -V 2 do not. Consequently, adding -Y is only useful for the highest three VBR settings."

http://wiki.hydrogenaud.io/index.php?title=LAME_Y_switch

I don't know if this has changed specifically in 3.100, but in any case. Wouldn't it be easy to test if the flag is ignored?

If the flag is in fact ignored and all other settings are the same, shouldn't the result file be an exact bit by bit copy?

Re: LAME VBR Settings and the Y Switch

Reply #4 – 2018-03-30 23:43:53

I did some playing around with -V 2 and --lowpass 16 and the -Y switch.  Turns out that they both create different MP3s than just the plain -V 2 switch.

However - from what I can tell - setting a quality algorithm of 0 (highest quality) doesn't seem to change anything with the VBR settings - I could be wrong though.

Re: LAME VBR Settings and the Y Switch

Reply #5 – 2018-03-31 00:41:41

"Other ways to say it include:
The -Y switch tells LAME to not be so strict with the higher frequencies, if they are going to cause an increase of bitrate."
Do not the "if", LAME may decide (or not) to use coarser encoding of high frequencies. If it thinks it has enough bits it spend then on better encoding of the higher frequencies.

To put it another way, it's opportunistic.  So by setting the -Y switch for V0/V1/V2, LAME may choose not to use it for certain packets (Note. I haven't checked the code, but I trust the Wiki knows more than me with that "if" there.).