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Topic: upsampling vs AC3 encoding question (Read 8063 times) previous topic - next topic
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upsampling vs AC3 encoding question

I am about to compile all my Pat Metheny's Cd's into one big DVD using the DVD Video as Audio trick, what i was wondering is which would give me the better quality - resampling from 44.1khz to 48khz and saving the audio as LPCM, or rather using a high bitrate AC3 compression, which is the lesser evil, upsampling or downcoding? Also am i better of allowing the Ulead program doing the resampling, or going with Adobe Audition?

upsampling vs AC3 encoding question

Reply #1 –
Well, proper upsampling is virtually lossless (if I had to guess, I would say that Adobe Audition has a pretty good upsampler). If there is room on your DVD for PCM then you must be able to fit a very high bitrate lossy compressed version so that is probably transparent as well, so either one seems safe. The only case where it might make a difference is in the unlikely event that you would decide to transcode those files to some other lossy format, in which case the PCM is definitely preferrable.

upsampling vs AC3 encoding question

Reply #2 –
Quote from: brb on
I am about to compile all my Pat Metheny's Cd's into one big DVD using the DVD Video as Audio trick, what i was wondering is which would give me the better quality - resampling from 44.1khz to 48khz and saving the audio as LPCM, or rather using a high bitrate AC3 compression, which is the lesser evil, upsampling or downcoding? Also am i better of allowing the Ulead program doing the resampling, or going with Adobe Audition?

You will need to resample anyway. The audio track needs to be 48 kHz.

LPCM would naturally be better because it is lossless. Can you fit all those CDs on a DVD disc if the format is LPCM? The wave files bitrate would be 1536 kbps at 48 kHz (before the DVD authoring process).

If you decide to use AC3 the audio track will be resampled and compresssed with a lossy codec.

Personally, I have no experience of the Ulead resampler's quality, but I would trust Audition more. It is essential to use Audition with right settings for getting best possible results.


EDIT added the "before authoring process" part. I guess the VOB format adds a few bits, but I have not actually tried what happens.

upsampling vs AC3 encoding question

Reply #3 –
As Alex B has already said, it is a requirement that whether you use LPCM, or AC3, the audio must be resampled to 48kHz.

From my own experiences, although you should try for yourself, AC3 @ 384kbps, stereo is very acceptable but only if you use a 'proper' Dolby encoder. The 'free' ones are adequate for movies, but really don't cut it where 'listening' is the main objective.

On Rarewares, Others page, you'll find the latest version of SRCdrop which uses the latest libsamplerate libraries. If you're looking for a simple, high quality resampler it doesn't get any simpler and the latest libs are very good.

upsampling vs AC3 encoding question

Reply #4 –
I'd trust Adobe Audition over Ulead...  I don't own Audition, but I do own a few Corel/Ulead programs.

That said, upsampling is pretty simple, and there probably isn't any difference.

I do have a strange problem with the Ulead AC3 encoder (fully-licensed, of course).  If I don't reduce the audio level, I get distortion.*  So, my standard procedure is to set the Ulead volume slider at "75%" before encoding/transcoding. 

To me this is weird...  You should never get clipping with a digital-to-digital conversion!  It might have something to do with the AC3 metadata causing clipping at playback time...      If I recall correctly, there is something in the AC3 format to set the "dialog" level (somewhat like ReplayGain does???).  Ulead does not give you any control over these "secret" settings.   

Most of these files are being transcoded from MPEG-2 audio, because that's what I get from my analog video-capture card.    But, I think I've had the same problem with WAV files and A/V files with LPCM audio.



* I assume it's clipping because it's most noticeable on the loud parts, and reducing the volume fixes it.  But, I've never decoded the AC3 and "looked-at" the waveforms.  (I just heard distortion on the loud parts and decided to reduce the level.)

upsampling vs AC3 encoding question

Reply #5 –
Quote from: DVDdoug on
I'd trust Adobe Audition over Ulead...  I don't own Audition, but I do own a few Corel/Ulead programs.

That said, upsampling is pretty simple, and there probably isn't any difference.

I do have a strange problem with the Ulead AC3 encoder (fully-licensed, of course).  If I don't reduce the audio level, I get distortion.*  So, my standard procedure is to set the Ulead volume slider at "75%" before encoding/transcoding. 

To me this is weird...  You should never get clipping with a digital-to-digital conversion!  It might have something to do with the AC3 metadata causing clipping at playback time...      If I recall correctly, there is something in the AC3 format to set the "dialog" level (somewhat like ReplayGain does???).  Ulead does not give you any control over these "secret" settings.   

Most of these files are being transcoded from MPEG-2 audio, because that's what I get from my analog video-capture card.    But, I think I've had the same problem with WAV files and A/V files with LPCM audio.



* I assume it's clipping because it's most noticeable on the loud parts, and reducing the volume fixes it.  But, I've never decoded the AC3 and "looked-at" the waveforms.  (I just heard distortion on the loud parts and decided to reduce the level.)

If you're creating AC3 audio for DVD creation from a wave/other source, I'd suggest to replaygain to 83dB, or -6dB from standard, as DVD players apply a significant boost on playback.

upsampling vs AC3 encoding question

Reply #6 –
Quote
If you're creating AC3 audio for DVD creation from a wave/other source, I'd suggest to replaygain to 83dB, or -6dB from standard, as DVD players apply a significant boost on playback.
  Uhhh....  My DVD player and receiver don't recognize ReplayGain tags.  It's not part of the Dolby AC3 standard and  I've never attemped to put a ReplayGain tag in an AC3 file...

I did a quick search, and the Dolby AC3 gain-adjustment "tag" is called dialnorm (dialog normalization).  Since its part of the Dolby standard, any reciever's AC3 decoder will utilize it.

It turns-out that dialnorm cannot increase gain at all...  The gain-adjustment range is from zero to -30dB.  So unlike ReplayGain, the dialnorm setting can't drive the DAC into clipping.

And like I said, Ulead doesn't allow the user select the dialnorm value and it doesn't tell the user what "secret" value it's using...  All you have (for gain adjustment) is a 0-100% slider (or maybe it goes over 100%... I can't remember...).  I assume 100% means "no change", but who knows...


P.S.  Sorry brb, I've drifted off-topic.. My main point is - Don't "blindly" trust the Ulead AC3 encoder.

upsampling vs AC3 encoding question

Reply #7 –
Quote from: DVDdoug on
Quote
If you're creating AC3 audio for DVD creation from a wave/other source, I'd suggest to replaygain to 83dB, or -6dB from standard, as DVD players apply a significant boost on playback.
  Uhhh....  My DVD player and receiver don't recognize ReplayGain tags.  It's not part of the Dolby AC3 standard and  I've never attemped to put a ReplayGain tag in an AC3 file...

I did a quick search, and the Dolby AC3 gain-adjustment "tag" is called dialnorm (dialog normalization).  Since its part of the Dolby standard, any reciever's AC3 decoder will utilize it.

It turns-out that dialnorm cannot increase gain at all...  The gain-adjustment range is from zero to -30dB.  So unlike ReplayGain, the dialnorm setting can't drive the DAC into clipping.

And like I said, Ulead doesn't allow the user select the dialnorm value and it doesn't tell the user what "secret" value it's using...  All you have (for gain adjustment) is a 0-100% slider (or maybe it goes over 100%... I can't remember...).  I assume 100% means "no change", but who knows...

Sorry, I was suggesting that the audio 'gain' should lowered prior to encoding into AC3.

upsampling vs AC3 encoding question

Reply #8 –
Thank you all for your good input!

@Alex B - good point i forgot that AC3 needs a 48khz sample rate anyhow.

@DVDdoug - The majority of consumer software encoders use -27db Dialnorm as default value, As this is the recommended "thumb rule" by Dolby. If you want no Dialnorm to be applied, set it to -31 and not 0 as this is a common mistake. read this great article about Dialnorm:

http://www.hometheaterhifi.com/volume_7_2/...ion-6-2000.html

upsampling vs AC3 encoding question

Reply #9 –
Quote from: john33 on
From my own experiences, although you should try for yourself, AC3 @ 384kbps, stereo is very acceptable but only if you use a 'proper' Dolby encoder. The 'free' ones are adequate for movies, but really don't cut it where 'listening' is the main objective.

Have you tried to ABXing "Aften -b 384"? Given that LAME (in general) is transparent @192kbps, are you saying that Aften AC3 sounds worse even when encoded at DOUBLE bitrate (384)?

upsampling vs AC3 encoding question

Reply #10 –
Quote from: tycho on
Quote from: john33 on

From my own experiences, although you should try for yourself, AC3 @ 384kbps, stereo is very acceptable but only if you use a 'proper' Dolby encoder. The 'free' ones are adequate for movies, but really don't cut it where 'listening' is the main objective.

Have you tried to ABXing "Aften -b 384"? Given that LAME (in general) is transparent @192kbps, are you saying that Aften AC3 sounds worse even when encoded at DOUBLE bitrate (384)?

I'll admit to not having tried it recently.  The last time I tried it was several years ago and the difference then was very marked but things may have changed. May be I should have another look at it.
 

upsampling vs AC3 encoding question

Reply #11 –
Quote from: john33 on
Quote from: tycho on

Quote from: john33 on

From my own experiences, although you should try for yourself, AC3 @ 384kbps, stereo is very acceptable but only if you use a 'proper' Dolby encoder. The 'free' ones are adequate for movies, but really don't cut it where 'listening' is the main objective.

Have you tried to ABXing "Aften -b 384"? Given that LAME (in general) is transparent @192kbps, are you saying that Aften AC3 sounds worse even when encoded at DOUBLE bitrate (384)?

I'll admit to not having tried it recently.  The last time I tried it was several years ago and the difference then was very marked but things may have changed. May be I should have another look at it.

Don't want to compare apples with peaches here: 384 or 448 kBps are the standard bitrates for multichannel AC3 movie soundtracks, if used for stereo it should give (not ABXed though) a pretty decent result. 192 kBps should then be fine as well, but, as stated before using an official (approved) encoder.
On the other hand: how many CDs of Pat Metheny would you like to "transcode" ? 5 - 6 will fit on a single layer DVD uncompressed (PCM) ...