Aften bitrate/ output frequences

[raquete]

afraid to be off topic in Aften thread i did a new one.

after heard differences i did this screenshots and the sound is really different.

source 5.1 wave(24b/48K) encoded with Aften R483(WavToAC3Enc) at 448k bitrate
http://img299.imageshack.us/img299/3108/w448.png

same source at 640K
http://img141.imageshack.us/img141/7932/w640.png

why this limitation in round 16.5KHz when encoding at 448K bitrate?!? this don't seems correct!

[Blue_MiSfit]

Erm.. there's only one image :)

~MiSfit

[raquete]

Erm.. there's only one image :)

~MiSfit

lol...:p
no, have 2!
imageshack delay to load the image for unknow reasons, :mad:
just wait a little or right click/show image.

encoding same source with sound forge in 448k(AC3 5.1).
frequences going better than with Aften in 448K
http://img35.imageshack.us/img35/2088/wsf448.png

Dolby "swear" that 448K can go to 20KHZ but....???
i can be wrong and Aften could be better in this bitrate.

[Blue_MiSfit]

It shows properly now :)

Indeed, I see what you're talking about... Quite surprising. You're certain you encoded the same source, and that you did in fact encode at 448kbps?

~MiSfit

[raquete]

It shows properly now :)

Indeed, I see what you're talking about... Quite surprising. You're certain you encoded the same source, and that you did in fact encode at 448kbps?

~MiSfit
i'm surprised too because i only use to encoded at 640k but to author in DVDLab is needed to encode at 448k, don't work with 640K(error).after heard 448k i feel something wrong and comparing in pc with winamp, saw the differents and the reason of what i am hearing...640 sounds better(more brilliant) and show more high frequences as the pictures are showing.
AC3 from sound forge at 448k is a little better than Aften at 448k, you can feel differences too.

and yes, same source(24b/48k), encoded at 448k and 640k with Aften and same source encoded with sound forge(only have option to 448k, is default for dvd and impossible to change)
if you want i can send the files(Rapidshare link) to remove all doubts.

cheers!

[raquete]

Blue_MiSfit,
The 3 AC3 files samples with ~30 seconds are so short, please download here:

AC3 samples (http://rapidshare.com/files/272365767/samples.rar) (6575 KB)
(AC3 5.1 from Aften 448k, Aften 640k and Sound Forge 448K)

hear and see differences. :)

[poisondeathray]

audacity shows the same thing (analyze=>plot spectrum) as your winamp graph

[tebasuna51]

The quality isn't only the bandwidth.
Aften use the max bandwidth for 640 Kb/s but you can use the parameter -w to control the bandwidth:

Aften -b 448 -w 60 sample.wav sample_448_max_bandwidth.ac3

EDIT:
To obtain the same bandwidth than Sound Forge try with -w 45 and -w 50 to be near 20 KHz

[raquete]

The quality isn't only the bandwidth.
Aften use the max bandwidth for 640 Kb/s but you can use the parameter -w to control the bandwidth:

Aften -b 448 -w 60 sample.wav sample_448_max_bandwidth.ac3

EDIT:
To obtain the same bandwidth than Sound Forge try with -w 45 and -w 50 to be near 20 KHz

EncWAWToAC3 adjusting bitrate 448k and Maximum Bandwidt 60

http://img44.imageshack.us/img44/4056/w448b60.png

:D the great tebasuna51 knows everything!

thanks so much tebasuna.

[Blue_MiSfit]

Interesting! I wasn't aware you could control these parameters. I was under the impression that the bandwidth:bitrate was part of the AC3 spec, not an encoder adjustable option!

~MiSfit

[SquallMX]

AC3Filter "Decoder info" section can give you the frecuency cut data for AC3 files.

SoundForge AC3 Encoder Frecuency Cut:
384 Kbps, 5.1 Channels: 10/18 Khz
448 Kbps, 5.1 Channels: 14/20 Khz
512 Kbps, 5.1 Channels: 17/20 Khz
576 Kbps, 5.1 Channels: 20/20 Khz
640 Kbps, 5.1 Channels: 20/20 Khz

Aften AC3 Encoder Frecuency Cut:
384 Kbps, 5.1 Channels: 14 Khz
448 Kbps, 5.1 Channels: 17 Khz
512 Kbps, 5.1 Channels: 19 Khz
576 Kbps, 5.1 Channels: 20 Khz
640 Kbps, 5.1 Channels: 23 Khz

:helpful:

[raquete]

EncWAWToAC34.1(Aften R832) Bitrate 448K(CBR), Maximum Bandwidth 60, 5.1 channels.

AC3Filter "Decoder info" 23kHz/23kHz

:cool:

[Blue_MiSfit]

I've heard some samples from Dolby that are 5.1ch, difficult music samples, but have full 23KHz bandwidth at 384kbps! They sounded reasonably good..

~MiSfit

[raquete]

very interesting Blue_MiSfit.

this samples at 384kbps are free? if ( do you have links? )

[Blue_MiSfit]

I don't think they're free. They were part of a qualification test package that my company received from Dolby in order to qualify equipment on perfect DD / DD+ decoding and sync etc...

I can't really post them :(

You can create the same kind of file with Aften by specifying full bandwidth, as was done earlier in the thread.

~MiSfit

[ronnylov]

Reducing bandwidth at lower bitrates may increase the audio quality just like reducing video resolution may increase quality at lower bitrates of video encoding. So maybe there is a reason why the bandwidth is limited? But maybe it is limited too much for these bitrates?

[Blue_MiSfit]

I believe the lowpass settings are chosen for good reason. Perhaps the older Dolby encoders weren't so good at (for example) 384kbps up to 20KHz, so they lowpassed the input to 18KHz (I think?) to improve overall quality.

As is the case with most things lossy compression related, it's all a tradeoff, and is highly source dependent! :) I personally believe that Aften's defaults are a bit conservative. I would expect 448kbps to preserve full 20KHz in any case.

Also note that spectrographs aren't really representative of percieved audio quality, in the same way that PSNR / SSIM aren't necessarily representative of percieved video quality. There are certainly some psy optimizations happening!

~MiSfit