Why is Alt-Preset ABR so fast?

[steerpike]

I converted the same wave file twice, using release 11 of dbp, lame 3.96.

First time, I used 'alt preset abr', with a setting of 160 kbps. The conversion was FAST - 14x or so.

Then I tried 'very high', with a setting of 'stereo', 'average bitrate', 160 kbps. This took a long time - 0.7x or so.

The end result were two almost identically sized files. The 'actual' bitrate showed as 163 for the 'alt abr' file, while the 'very high' version was 155.

The only substantial difference I can see is that the 'alt preset abr' version enforces 'joint stereo', but I'm assuming that's not the issue.

My preference is to use the 'very high' approach, because I want to select 'stereo' rather than 'joint stereo', but this time difference is very large!

Thanks!

[xoas]

Re: Why is Alt-Preset ABR so fast?

What you might want to do is to set the mp3 conversion to No Preset, Average Bitrate, stereo, 160. This is nearly as fast as the alt ABR 160 preset but allows you the stereo opotion. No preset, Average Bitrate, jopint stereo is about as fast as the alt ABR preset.
Make sure to try comparing a couple of different files and listen to them to make sure you aren't introducing any noticeable difference in the quality of your conversions (probably you will not be, but better safe than sorry).
Best wishes,
Bill Mikkelsen

[steerpike]

Re: Why is Alt-Preset ABR so fast?

Thanks - I did not see the 'no preset' option until you mentioned it. Based on your suggestion, I tried exactly what you said (no preset, ABR, 160 kbps, stereo) and got an 11x conversion. I then set 'normal' encoding, all other settings the same, and got an 11x conversion. I then set 'high' encoding, all other settings the same, and got an 11x conversion. I then set 'very high' encoding, all other settings the same, and got a 0.7x conversion !

I'm really just trying to learn the (excellent!) program at the moment. I don't mind waiting for the longer conversion if the quality is significantly better. I've spent the best part of the day trying various settings, ranging from CBR through VBR and now ABR. I understand the advantage of VBR/ABR over CBR, but I was put off VBR by the unpredictability of the output rate. I tried, for example, VBR 80-192 kbps, and was surprised to get resultant (net) bitrates of 180+; I was assuming that the average net rate would be close to the mid-point, but it was not - so be it. So now I'm focusing on ABR.

Regarding ABR - is there any way to know what max and min rates are used? In the video world, you can set the target 'average', but also specify the upper and lower limits.

But anyway, my question is now, perhaps, why switching from 'high' to 'very high' makes such a huge difference. I'm wondering if this is some new behavior associated with the release 11 and/or Lame 3.96; I was testing with release 9, lame 3.92 this morning and never saw this kind of behavior.

Is there a way to see the actual command line passed to the encoder?

Thanks!

[LtData]

Re: Why is Alt-Preset ABR so fast?

Regarding VBR, it find the best bitrate based on the limits you give it. The higher your upper limit, the higher the bitrates it can use. How did this put you off? Personally, I think VBR is the best way to go, as you get the bitrate you need at each second and little more.

[steerpike]

Re: Why is Alt-Preset ABR so fast?

I was 'put off' VBR because it seems to choose a bitrate 'close to' the upper limit each time, and the resultant filesize is larger than I 'expected' (see below for more info on this).

I must admit, I was expecting an 'ABR'-like behavior from VBR in that, I expected it to yield an average close to the mid-point between upper and lower. Since I can achieve that with ABR, I can look to ABR if I want that behavior. The only problem with ABR is that the dBpowerAMP user-interface does not seem to allow me to specifiy the upper and lower limits. Ideally, I'm looking for something I'm used to in the video encoding world (TmpegEnc) whereby I specify the average, low and high points.

I've since downloaded lame.exe 3.96.1, and beSweetGui, which allows me to 'construct' the command lines very easily. After experimenting I realise now that the 'VBR quality' flag (-V, not to be cofused with the noise shaping quality flag, -v! - CORRECTION - noise shaping quality is -q, not -v!) affects the overall bitrate profile of the output. If I leave the flag off completeley, I get a resulting average that's 'about half-way' between upper and lower. But if I set '-V 0', I get a resulting average very close to the upper limit. I'm guessing, therefore, that using the 'Very High' profile in dBpowerAMP sets the '-V' to a high quality setting.

I also answered my question about 'time taken' - I noticed that, if I set a 'noise shaping quality' value of 0 ('-v 0' CORRECTION: '-q 0'), I can see the same huge increase in time, so I'm guessing that 'very high' in the dBpowerAMP profile sets a '-q' of '0'.

I'm guessing there is no way to know what switches are used by dBpowerAMP for the profiles such as 'Very High'?

[xoas]

Re: Why is Alt-Preset ABR so fast?

I'm guessing there is no way to know what switches are used by dBpowerAMP for the profiles such as 'Very High'?

I'm not entirely sure there is. The alt presets are based on Dibrom's switches and my understanding is that the other presets were native to Lame, but I could be wrong about this.

But if you are comfortable in your understanding of Lame's command line interface you could download the Lame command-line interface codec from Codec Central and program the settings you want.

Best wishes,
Bill Mikkelsen

[steerpike]

Re: Why is Alt-Preset ABR so fast?

One final question ... ...

Is there a reason that the dBpowerAMP does not support the "medium" 'alt preset'? 'medium' seems to offer a decent compromise.

[LtData]

Re: Why is Alt-Preset ABR so fast?

You will have to use the LAME.exe CLI codec to use the medium preset.

[LtData]

Re: Why is Alt-Preset ABR so fast?

Also, one more thing to remember: Higher-quality encoding or higher-levels of compression take longer. Encoding to Extreme Monkey's Audio will take longer than encoding to 64kbps mono mp3.