Hydrogenaudio Forums > ABR and lowpass?

guidryp

Sep 9 2003, 11:48

How do the ABR presets work ( alt-preset 144 )?

I encode my CD's at APS -Y. I can't even hear a frequency sweep at 16KHz, so music in that range is irrellevant to me.

Now I want to transcode specifically for my portable (ONLY has 96MB) and would like something better than ABR 128 which still sounds like crap on many tracks even in a portable.

So I am thinking about AP 145. Now as an ABR rate I believe there is a low pass already built in? Does anyone know what it is? Any benefit from using a lower one, since for me any cutoff over 16K would be a waste.

I am curious about the ABR rates, the ALT preset 8-320. Surely these can't be specifically tuned for each and every number 128, 129,130 etc. They must have ranges they work in with similar setups (lowpass etc..).

Then again this may be moot since my originals are probably lacking above 16KHz.

I figure transcoding is probably frowned on but this is strictly for my Portable.

Peter

music_man_mpc

Sep 9 2003, 12:09

I am no expert, however, I think your safest bet would be --alt-preset 160. Applying a different lowpass than the default could potentially compromise tuning and the difference between 145 and 160 should be bareable

. Maybe you could also try --alt-preset medium or --alt-preset medium -Y (if this helps for medium). Try all these out, but most importantly trust your ears for deciding which setting is the best.

My other suggestion would be to avoid transcoding if AT ALL possible. You may find --alt-preset 128 just fine if you encode from a fresh source.

dev0

Sep 9 2003, 12:30

AFAIK the -Y switch is already included in medium and would probably cause the opposite of the desired effect.

-Y used on --alt-preset standard does not cause a 16khz lowpass, but only changes the way content over 16khz is handled by lame. There still is content over 16khz in an --alt-preset standard -Y encoded file and the lowpass is still at 19khz like vanilla aps.

--alt-preset 128 has lowpasses at 17khz and should fit your needs just fine. If you are really not sensible to content over 16khz, you could also try using ff123's 128kbps ABR cmd.line:

CODE

--abr 128 -h --nspsytune --athtype 2 --lowpass 16 --ns-bass -8 --scale 0.93

dev0

john33

Sep 9 2003, 13:13

The more significant differences in the ABR presets are:

CODE

// kbps Z X lowpass safejoint nsmsfix ns-bass scale
{ 8, 1, 6, 2000, 0, 0 , -3, 0.85 }, // 8 //impossible to use in stereo
{ 16, 1, 6, 3700, 0, 0 , -3, 0.85 }, // 16
{ 24, 1, 1, 3900, 0, 0 , -3, 0.85 }, // 24
{ 32, 1, 1, 5500, 0, 0 , -3, 0.85 }, // 32
{ 40, 1, 1, 7000, 0, 0 , -3, 0.85 }, // 40
{ 48, 1, 1, 7500, 0, 0 , -3, 0.85 }, // 48
{ 56, 1, 1, 10000, 0, 0 , -3, 0.85 }, // 56
{ 64, 1, 1, 11000, 0, 0 , -3, 0.85 }, // 64
{ 80, 1, 1, 13500, 0, 0 , -3, 0.85 }, // 80
{ 96, 1, 1, 15300, 0, 0 , -4, 0.85 }, // 96
{ 112, 1, 1, 16000, 0, 0 , -5, 0.87 }, // 112
{ 128, 1, 1, 17500, 0, 0 , -6, 0.93 }, // 128
{ 160, 1, 1, 18000, 0, 0 , -4, 0.95 }, // 160
{ 192, 1, 1, 19500, 1, 1.7 , -2, 0.97 }, // 192
{ 224, 1, 1, 20000, 1, 1.25, 0, 0.98 }, // 224
{ 256, 0, 3, 20500, 1, 0 , 0, 1.00 }, // 256
{ 320, 0, 3, 21000, 1, 0 , 0, 1.00 } // 320
};

The setting used is that one that is arithmetically closest to the ABR bitrate specified.

sven_Bent

Sep 9 2003, 13:41

QUOTE(john33 @ Sep 9 2003, 08:13 PM)

The more significant differences in the ABR presets are:

CODE

BLAH
BLAH
BLAH

The setting used is that one that is arithmetically closest to the ABR bitrate specified.

why sudenly the nsmsfix for 2 settings and then gone again ?

guidryp

Sep 9 2003, 13:48

I have tried 128 from a clean source and I still have a problem with it. Transcoded 140 still sounds better than clean 128 IMO.

QUOTE

The setting used is that one that is arithmetically closest to the ABR bitrate specified.

Thanks for the table John. Is it just me, or does 17.5KHz seem awfully high at 128.

Lately I have taken to actually using APS with lowpass 16, as I can't hear the difference and it saves a few more bits. Still average about 180-190K it seems. Really would like about 140 for the portable.

So it seems like 17.5 K with 128K will be full of artifacts...

Still one question remains. What happens if I try to apply my own cut-off to the ABR presets?

Say alt-preset 140 --lowpass 16. Is it smart enough to either save bits or make better use of bits? I can't see it doing that much harm. I guess I will test later tonight.

Peter

john33

Sep 9 2003, 15:37

Dibrom constructed the table, so he is the one with the answers.

guidryp

Sep 9 2003, 16:46

Hmmm. I did a test with a live metal track (all from the WAV):

APS 210Kbps
APS -lowpass 16 196Kbps

AP 140 = 135Kbps
AP 140 -lowpass 16 = 135Kbps (actually this file was a few K larger)

I couldn't tell them apart for sound quality either. So lowpass seems to have no effect here anyway...

magic75

Sep 10 2003, 02:10

I could be way off here but...
I don't think that the fact that -ap 128 uses lowpass 17.5 means that all frequency content up to that is necessarily reproduced. The presets use this nsbass switch which i think is used to give more bits to lower frequencies when needed. By listening (I think) I have heard that tracks with large stereo separation lose more in the upper frequencies than those with narrow stereo separation. And I shouldn't really be able to hear above 16 kHz in real music so...