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how to get the lower bitrates?
post Jan 12 2002, 19:46
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So, I would like to have mp3 files close to 192 kbps. I listen mostly metal (various types - heavy, power, black, ...) and --alt-preset standard seems to create mostly bitrates of 200-250 (tested with several albums). I consider this to be too high, how should I create the files to get lower rates? Should I use ABR with --alt-preset [rate] or maybe some VBR command line (for example, edited -r3mix), using -V[n] to adjust the bitrates? Any suggestions?
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post Mar 12 2002, 00:21
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Originally posted by mp3fan
So by using a --lowpass 17.5 & -Y, I'm telling the encoder that when it does "bother to encode" freqs above 16k, it won't go beyond 17.5, right?

Yes, though it's kind of pointless to do this because very rarely does anything over this point get encode, and when it does, it doesn't really increase the bitrate.

[b]You're former description seems to indicate that it won't encode ANYTHING beyond 16k while your prior statement indicates that some material beyond 16k will get encoded.  Please explain.

Note the clarification as "very rarely does it encode over 16khz, and when it does, it doesn't increase the bitrate".

[b]Also, when I use an [b]--athlower number up to 8, --athlower 8, there is no change in bitrate and I expected to see a filesize increase with this setting.

I'm not sure what the problem is there, it should work. What's the full command line you are using? And did you verify that for sure this switch is being passed to the encoder by trying it on the command line instead of through some sort of frontend?

Also, what is the effect of using [b]-Y with ABR or CBR?  Will it still work the same way in those modes?

No, because CBR and ABR do not increase the global gain (quantziation stepsize accuracy) to encode these frequencies in the manner VBR does. So both -Y doesn't do anything, and CBR/ABR don't have bitrate issues with sfb21 either.

Also, a small note which may be relevant, although I've stated it many times before, it seems people keeping forgetting this. At any rate, when content over 16khz is encoded, and it causes such a big jump in bitrate, the majority of the extra bits aren't actually being spent on the frequencies over 16khz. Instead they are being spent on all the frequencies below this point.

The reason for this is as follows. sfb21 is the scalefactor band which is assigned to the frequencies beyond 16khz. However, the problem is that it doesn't actually have a scalefactor, or basically a way to efficiently compress these frequencies, while all other sfbs do. Apparently, this was an oversight in the design process of the format, because either the developers thought frequencies beyond 16khz were inaudible (or irrelevant), or as robert suggested, maybe the format was designed for 32khz PCM as is used on DAT, which resultingly goes up to this frequency. In any case, to actually encode these frequencies then, you have to increase the resolution of all of the sfbs, so that you can "in effect" also control the resolution of sfb21 (which, because of a lack of a scalefactor, you cannot control independently). Make sense?

So what's happening when VBR spends massive bits when lots of 16khz content is present, is the bits are actually mostly being spent below these frequencies... so there's not really the problem (which seems to be a common misconception) of too many bits being spent on 16khz+ frequencies at the expense of the lower ones.

As for why I don't recommend using -k then, it's not actually because of too many bits being spent on the wrong frequencies, but more so that encoding irrelevant content could lead to more problems, like for example, maybe using too many bits from the bit reservoir than is necessary on a particular frame, etc. There is also the possibility that encoding more content, but not accurately enough, could lead to more errors, which would not actually be noticed if the content wasn't present at all. As an example, it'd be better to cutoff at 16khz in a particular situation, than have a file that goes up to 17khz but where everything beyond 16khz may be effected by ringing (this is a hypothetical situation).
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Posts in this topic
- amppa   how to get the lower bitrates?   Jan 12 2002, 19:46
- - tangent   I would recommend only using --lowpass (try 17.5) ...   Jan 12 2002, 20:16
- - ami   hi, hmm since ive read, that dibrom listens and en...   Jan 12 2002, 20:25
- - amppa   So, if I got it right, lame --alt-preset [rate] sh...   Jan 12 2002, 21:38
- - NeoRenegade   You got it dead on   Jan 13 2002, 23:46
- - TheBashar   I don't recall ever reading Dibrom say that with h...   Jan 14 2002, 00:56
- - Weiman   How about --alt-preset standard -V 3 -B 256? It gi...   Mar 7 2002, 21:29
- - Dibrom   My stance on this: Lowering the lowpass is by far...   Mar 7 2002, 21:57
- - mp3fan   QUOTE like employing an adaptive lowpass, with a l...   Mar 8 2002, 03:59
- - kxy   Newbie questions... when I use -alt-preset stand...   Mar 8 2002, 08:22
- - Sachankara   I still donīt see why you donīt use --alt-preset 1...   Mar 8 2002, 22:55
- - Dibrom   QUOTE Originally posted by mp3fan Currently [b]--...   Mar 8 2002, 23:42
- - kxy   Thx Dibrom. So despite the sfb21 warning, if some...   Mar 9 2002, 15:32
- - Dibrom   You don't need to use a lowpass when you use -Y. ...   Mar 9 2002, 19:10
- - kxy   Oh yea, of course I don't need to use -y and --low...   Mar 9 2002, 20:50
- - Dibrom   QUOTE Originally posted by kxy To recap, the -Y o...   Mar 9 2002, 21:03
- - mp3fan   Dibrom, QUOTE By using -Y, and disabling noise sh...   Mar 10 2002, 03:10
- - jkeating   You are forgetting about stereo settings! Right no...   Mar 12 2002, 00:04
- - Dibrom   QUOTE Originally posted by mp3fan So by using a -...   Mar 12 2002, 00:21
- - Dibrom   QUOTE Originally posted by jkeating You are forge...   Mar 12 2002, 00:24
- - ErikS   QUOTE Originally posted by Dibrom The reason fo...   Mar 12 2002, 02:28
- - JohnV   QUOTE Originally posted by ErikS No. Sorry for be...   Mar 12 2002, 03:30
- - Delirium   JohnV and Dibrom -- thanks for the explanations, I...   Mar 12 2002, 09:40
- - mithrandir   Considering that MP3s primary function is to reduc...   Mar 12 2002, 17:35
- - mp3fan   QUOTE Also, when I use an --athlower number up to ...   Mar 16 2002, 20:06
- - Dalkus   Reading through the FAQs and other threads I can...   May 4 2003, 16:30
- - SometimesWarrior   Using the -Y switch with --ap extreme carries the ...   May 5 2003, 06:36
- - Dalkus   Thanx for the reply. I'm just thinking that if...   May 5 2003, 13:30

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