Aac Audio: Please Check my Math!

kwag · #1 03-09-2006, 10:51 PM

Hello everyone

Could anyone verify my math here

I'm currently thinking about encoding a bunch of audio CDs to the newer aacPlus CODEC, so I can keep a DVD with all my music handy, and take it to work, etc. (And also hoping that a portable player supporting aacPlus (AAC+) hits the streets in the near future

)
So, using CalcuMatic and ignoring the Video fields, I figured that at 48Kbps (CD quality, as per specifications here: http://www.codingtechnologies.com/products/aacPlus.htm )

Quote:

Features
• True Superset architecture
• Multichannel support for 5.1, 7.1 and beyond (48 channels total)
• Built-in error concealment for mobile applications
• CD-quality stereo down to 48 kbps
• Near CD-quality stereo at 32 kbps
• Excellent quality stereo down to 24 kbps
• Widest available audio bandwdith
• Optimized speech, mixed speech/music down to 8 kbps mono
• Compliant with ISO/IEC 14496-3, incl. Amd.1:2003, Amd.2:2004, and all corrigenda

I should be able to put 8 days worth of CD quality audio on a single DVD

So please check my math

11520 minutes (8 days) ~24Kbps (CalcuMatic doesn't have 48Kbps, so use 24Kbps and multiply by 2 )

11520 minutes @24Kbps yields 2025000KB, times 2 = 4050000KB
With some room still to spare

So basically, this means that we can put 8+ days worth of CD quality audio on a DVD-5

-kwag

Dialhot · #2 03-10-2006, 05:11 AM

YOur maths are not so wrong despite the fact you are taking too much room

An other way to do your math :
A CD-Audio contains 80 minutes of PCM at 1411 Kbit/s.

1411/48 = 29.4. So a CD contains 29.4 x 80 minutes = 39.19 hours.

A DVD contains 6 CD, so 6 * 39.19 hours = 9.8 days !

GFR · #3 03-10-2006, 06:53 AM

Quote:

I figured that at 48Kbps (CD quality, as per specifications here:

CD quality per specification is not the same as real "CD quality". It's like MS telling you that wmv low bitrate videos are "DVD quality"

I've tried the Winamp AAC+v2 with SBR, parametric stereo etc. and while it's IMPRESSIVE, it's _not_ "CD quality". There are some obvious artifacts, even more obvious if you use headphones. It's more than good enough for background music or for listening through PC speakers, though.

There's a public listening test on various AAC codecs @ 48kbps going on, maybe some of you want to participate:

http://www.hydrogenaudio.org/forums/...howtopic=41598

http://www.mp3-tech.org/content/?48k...0public%20test

kwag · #4 03-10-2006, 10:28 AM

Quote:

Originally Posted by GFR

Quote:

I figured that at 48Kbps (CD quality, as per specifications here:

CD quality per specification is not the same as real "CD quality". It's like MS telling you that wmv low bitrate videos are "DVD quality"

I've tried the Winamp AAC+v2 with SBR, parametric stereo etc. and while it's IMPRESSIVE, it's _not_ "CD quality". There are some obvious artifacts, even more obvious if you use headphones.

Yes, but it's so close to the original, that if you don't have anything to compare (ABX test), even with earphones it sounds like the original. At l least it did to me

However, I'm sure that if I compare and switch back and forth between the audio CD and the 48Kbps AAC+, there will be some differences heard, just as you said.
At about what bitrate would you consider AAC+ to be transparent

I'd like to make some tests

But man

, the thing sounds so damn good, even at 24Kbps through speakers it's like FM radio, and at 32Kbps it's really like FM+ quality.

Quote:

It's more than good enough for background music or for listening through PC speakers, though.

Indeed

Quote:

There's a public listening test on various AAC codecs @ 48kbps going on, maybe some of you want to participate:

http://www.hydrogenaudio.org/forums/...howtopic=41598

http://www.mp3-tech.org/content/?48k...0public%20test

I'll check that out.
And if you or anyone knows of a portable player that can playback AAC+, please let me know

-kwag

kwag · #5 03-10-2006, 10:30 AM

Quote:

Originally Posted by Dialhot

YOur maths are not so wrong despite the fact you are taking too much room

An other way to do your math :
A CD-Audio contains 80 minutes of PCM at 1411 Kbit/s.

1411/48 = 29.4. So a CD contains 29.4 x 80 minutes = 39.19 hours.

A DVD contains 6 CD, so 6 * 39.19 hours = 9.8 days !

Good one Phil

-kwag

GFR · #6 03-10-2006, 01:52 PM

Quote:

Originally Posted by kwag

Yes, but it's so close to the original, that if you don't have anything to compare (ABX test), even with earphones it sounds like the original. At l least it did to me

Well, I can hear that something is strange even without comparing to the original. But I'm an amateur/semi-pro musician so I have a "trained ear" for tone/timbre.

Quote:

At about what bitrate would you consider AAC+ to be transparent

I'd like to make some tests

I don't know. I have not tested it. For mp3, I think 160kbps to 192kbps is perfect, it depends on the kind of music. I can definetely hear artifacts @ 128kbps. This is with heaphones. Through (big and good) loudspeakers 128k is Ok most of the time.

The innovations in AAC+ are more directed to very low bit rate (and they really achieve excellent results), not to transparent or hi-fi. Like SBR (where you throw off the highs and use the lows and mids plus some "clues" to create an artificial treble content). Or parametric stereo (you encode in mono and then use some clues to create a synthetic stereo). I guess because of that the bitrate for really "transparent" should not be much smaller than for mp3 - maybe 96k or 128k.

Quote:

But man

, the thing sounds so damn good, even at 24Kbps through speakers it's like FM radio, and at 32Kbps it's really like FM+ quality.

Yeah

kwag · #7 03-10-2006, 11:54 PM

Just to let you all know that I've decided on this: http://tcpmp.corecodec.org/about
Instead of waiting for a player

The Core Media Player, plays ALL audio formats, including AAC+ with plugin available here: http://www.rarewares.org/files/aac/t...almos.0.66.zip (PALM)
And here: http://www.rarewares.org/files/aac/t...obile.0.66.zip (Windows Mobile)
So we can play all types of audio and even video on any PALM or Pocket PC

Code:

Supported file containers
- AVI (*.avi)
- Matroska (*.mkv, *.mka)
- MP4 (*.mp4, *.m4a)
- Ogg Media (*.ogg, *.ogm)
- ASF (*.asf)

Supported audio codecs
- Mpeg 1 Layer III
- Ogg Vorbis
- Musepack
- Windows Media Audio (on Windows Mobile devices)
- AC-3
- AMR
- Adpcm, uLaw

Supported video codecs
- DivX
- XviD
- MPEG4-SP (plus B-frame support)
- MPEG1
- M-JPEG
- Windows Media Video (on Windows Mobile devices)

-kwag

Sagittaire · #8 03-11-2006, 10:45 AM

48 Kbps AAC (PS+HE) sound more like 96 Kbps MP3 with lame. Certainely not transparant because sbr is imo really destructive.

kwag · #9 03-11-2006, 01:36 PM

Quote:

Originally Posted by Sagittaire

48 Kbps AAC (PS+HE) sound more like 96 Kbps MP3 with lame. Certainely not transparant because sbr is imo really destructive.

Try the latest (current) AAC+ encoder version in Winamp 5.21. At 48Kbps, it sounds far better that any 128Kbps I've ever heard

-kwag

black prince · #10 03-11-2006, 08:56 PM

@Kawg,

Kwag wrote:

Quote:

Try the latest (current) AAC+ encoder version in Winamp 5.21. At 48Kbps, it sounds far better that any 128Kbps I've ever heard Exclamation

-kwag

I D/L'd Winamp v5.21, installed it and tried to play streaming music at
SKy.fm. I seem to connect and see the scrolling URL, but no sound is
playing. Should I set something in prefrences input / output plugins

I also, tried FooBar 0.9RC2 and again it wouldn't play. WMP did play
media audio on Sky.fm and was very nice.

-BP

kwag · #11 03-11-2006, 09:00 PM

Hi BP,

Foobar should play ANY aacPlus station

Try "Preferences/ File Types" on Foobar, and select "Associate all" button, just to test.
Then click on any of the links at www.tuner2.com to try it out

-kwag

black prince · #12 03-11-2006, 10:05 PM

@Kwag,

Kwag wrote:

Quote:

Hi BP,

Foobar should play ANY aacPlus station Exclamation
Try "Preferences/ File Types" on Foobar, and select "Associate all" button, just to test.
Then click on any of the links at www.tuner2.com to try it out Smile

-kwag

Works!!!!

Damn that sounds good

Thanks Kwag.

-BP

rds_correia · #13 03-12-2006, 09:16 AM

It does, doesn't it?

I can't stop hearing 4U - Rock n Metal.
That station rocks

.

GFR · #14 03-13-2006, 07:10 AM

Quote:

Originally Posted by kwag

So we can play all types of audio and even video on any PALM or Pocket PC

-kwag

Thanks for the links!

Now if I could use the Palm with a good stereo mic to "tape" concerts, etc. in a good quality format...

GFR · #15 03-21-2006, 07:28 AM

Quote:

Originally Posted by GFR

There's a public listening test on various AAC codecs @ 48kbps going on, maybe some of you want to participate:

http://www.hydrogenaudio.org/forums/...howtopic=41598

http://www.mp3-tech.org/content/?48k...0public%20test

The results are out:

http://www.mp3-tech.org/tests/aac_48/results.html

Quote:

Results comments

* Nero HE-AAC v1 scored quite higher than 3GPP HE-AAC v1, but considering 95% confidence intervals it can not be ranked higher than 3GPP: The top of 3GPP confidence interval has the exact same value as the bottom of Nero v1 confidence intervall. All the contenders are statistically tied.
* Considering the bitrate (48kbps), all the contenders performed quite well.
* The benefit of HE-AAC v1/v2 over plain AAC-LC (iTunes low anchor) is quite strong at this bitrate.
* By looking at the results of Nero and CT, which both have HE-AAC v1 and v2 modes, it seems that overall, plain HE-AAC might be better than HE-AAC v2 at this bitrate, but a lot more samples would be needed to be able to draw definitive conlusions regarding this.
* For a reference encoder, 3GPP scored quite well, as it is competitive with other state of the art implementations. Previous MPEG audio demonstration codes (MP3 and AAC) were notoriously bad.

kwag · #16 03-21-2006, 09:21 AM

I don't know if I'm missing something here, but the latest test I made (heard on my PC speakers) with LAME ( LAME 32bits version 3.98 (alpha 3, Mar 15 2006 06:00:39) )
even using "-V 7--vbr-new", are far better than any AAC/AAC+ at 48Kbps

Have you tested that

I know that the bitrate is higher, but it's still averaged below 128Kbps.
I can clearly hear AAC+ artifacts all over the place, but with LAME, therey're almost non-existant.
Just make sure you use version 3.98 alpha 3 of LAME.

-kwag

GFR · #17 03-21-2006, 12:13 PM

The LAME (3.97b2) -V5 encode @ ~130kbps is only included as a "high anchor" in this test - that is, it is not in the "competition", it is expected to be undoubtly better than any of the encoders under testing. The inclusion of a high anchor and a low anchor makes the statistical treatment easier.

If you see the final results, the LAME got 4.73/5, that is, almost perfect, while the AAC+ files are ~3/5, significantly worse than LAME, but at a smaller bitrate. Also the AAC+ is undoubtly better than the low anchor (AAC without the plus) that scored a very low 1.49.

So... my interpretation of the results is that AAC+ is obviously not near CD quality but it's much better than standard AAC and a good option when you need the lower bitrate.

It is interesting to see the full results to see how the encoders handle each sample.

Sagittaire · #18 03-21-2006, 07:29 PM

Quote:

Try the latest (current) AAC+ encoder version in Winamp 5.21. At 48Kbps, it sounds far better that any 128Kbps I've ever heard

My hear are good too ... last AAC HE V1 (from Nero or CT) sound like 80-96 Kbps MP3.

64 Kbps AAC HE V1 sound like 128 MP3 CBR (latest lame build) for my hear.

GFR · #19 03-22-2006, 09:14 AM

Quote:

Originally Posted by kwag

Just make sure you use version 3.98 alpha 3 of LAME.
-kwag

Just a warning: alpha versions of LAME are considered unstable and not recommended for anything but tests. If you want to keep the encodes, the developers recommend sticking to betas (stable). The last recommended version is 3.97b2.

kwag · #20 03-22-2006, 10:00 AM

Thanks GFR

-kwag