I realize that this is not a scientific test, but in another thread people expressed interest in the differences in HE and LC-AAC 5.1 encoding with Nero, and I also had questions, so I made a little test for people to listen to.

These files were encoded with Nero Recode 2. They are in .mp4 format and were encoded with the new AVC encoder so as not to take alot of space. Don't worry, they will play in VLC and most other good players.

Files for download:
##5.1_Test##.txt - This page gives details on each of the files.
Downloadable's - Here you can grab the various files and hear for yourself.


Now for my personal evaluation:

If you don't feel like downloading them all, just get files 1, 3, and 5.

Basically what I found is that HE-AAC is no good if you're looking for just "good" audio. It has problems with high-frequency sounds and creates distortions. The effects remind me of streaming audio distortions. Oddly enough, the lowest bit-rate (128Kb) HE-AAC file sounds better than the 192Kb version. The best file would be either #5 or #6. I was unable to discern a difference between the two.

In the end, it seems that for good 5.1 sound, it's LC-AAC all the way. 192 or 256 both produce good sound. Sampling rate doesn't seem to matter (for LC).

One issue that I will end with is that Nero seems to give inconsistent results. When encoding longer video clips (i.e. whole movies) the audio quality will temporarily degrade, but only when using HE-AAC. I have not the knowledge to explain why, but it does.

LC-AAC wins for me.

Thank You in adavnce for your comments and technological knowledge. I'm sure that I'll learn alot from the ensuing discussion.

Instead of 5 video clips, it would really have helped to just have a small clip of the source (not encoded) audio alone. Right now all I can do is have listen to the clips, conclude there are no gross artifacts, and that's it.

So basically, I can't verify any of the supposed "problems" you are reporting.

One of the biggest problems is that there are intermittent drops in audio quality when a longer file is encoded. As for the audio quality, i'll try to rip the same clip into straight 2 channel PCM. Hopefully that will give you a good reference.

I can also cut the same scene from the fully encoded film. This will show much more accurately all of the artifacts that seem to only occur in a longer encode.

Thanks for the reply!

Is the source AC3 or PCM? This looks like a DVD, after all.

We just found a bug in the 5.1 encoder - so quality drops are indeed there.

This behaviour is clearly a bug and it will be fixed in the fastest possible time.

That's great to hear Ivan!

Before I say anything else, it may have come off as me being a punk or something, so let me set the record straight. I am an extremely satisfied Nero user. If it was a woman, i would have sex with it (maybe). This is the only problem that I have ever had really!

Now for more, the source is DVD PCM. I cannot rip it into 5.1 PCM because I don't know how (I'm fairly amateur if you haven't noticed). I can convert it into a stereo PCM file (.wav extension).

Since you pointed out that this is a bug, maybe I can help you examine it. I'll cut the file that I ripped the whole film to (HE-AAC 5.1 192Kb 48,000khz) and you can look at it side by side with the short clip that I have already posted with the same audio quality. This is where it is easy to hear the problems. All I have to do now is figure out how to split a .mp4 file . I'll try to have them upped by this evening.

I really do appreciate the info. I'm interested to know what happens when encoding a longer file at the same settings that makes the quality different.

MPEG4IP utilities split the tracks out from mp4 to aac:
http://rarewares.org/mp4.html

But maybe you meant you wanted to split out a portion of the whole file?

After searching google I found this, which recommends quicktime or mp4box:
http://forum.doom9.org/showthread.php?p=636032#post636032

MP4Box splits MP4 (AAC, ASP, AVC, TTXT, MPEG-1/2, private streams) time- and sizewise, extracts parts and joins MP4 too
- Ulead's VideoStudio 8 with the MPEG-4 plugin
- Sony's Vegas 6
- Quicktime/Pro can be used to create (encode, mux) and edit (split, join) MP4 files, supports MPEG-4 Simple Profile, AAC, AVC

OK!

I figured out how to do the cutting and I have an uncompressed piece of the original source!

I've upped them to the original downloadables page.

FullFilmEncode-HE-AAC 192Kb 48,000khz.mp4 - A cut piece of the fully encoded film.

Nero 5.1 Test #1-3.mp4 - The small clip that I originally posted for this test that was encoded with identical audio quality settings as the above piece.

SourceAudio.wav - Un-compressed audio from the original source (DVD).

While the SourceAudio clearly has advantages, I would be content if the full-film had the same quality as the sample, but it does not. I realize it may not be that bad, but I play the films that I watch loud over a quality surround system. At those volumes, the effects are evident.

There are several places where there are high-frequency distortions, one place to look if you can't hear them (yeah right, you guys are audiophiles) is right when the second pilot's parachute opens.

Thanks again. I hope this is useful to you in finding the bug.

Any new info Nero guys?

The bug was identified in the beginning of month already and it's known. So don't worry, fix is coming.
Before this is fixed, I don't recommend using 5.1 channel AAC-HE with the recent encoder, cause the quality drop can be pretty significant for some people.. Use 5.1 LC instead for now.

Thanks for the info. I'll be on the lookout for the fix .

I have been encoding DVD AC3 audio using Nero Digital from the Nero 7.0.1.2 ultra pack quite a bit lately and I haven't noticed any bug whatsoever. I'm not quite sure what you mean by those 'quality drops'.

I'm quite satisfied with:
- HE-AAC @ 225kbps for low bitrate encodes. Although to me (TOS#8 warning) it has obvious hissing in speech containing s-sounds (and English seem to have quite a bit of those ), it's quite acceptable. I realize this is an fairly high setting for HE-AAC.
- LC-AAC @ 320kbps. I just can't tell the between de encode and the original AC3. I should try abx-ing @256kbps again with the new encoder though.

Concerning the audio side of Nero Digital I only have two problems: First, no possibility of using DTS as the source but second, and this surprised me lately, there is no possibility of encoding a mono source to mono!

If you are encoding smaller clips (not an entire 1.5h+ film) you will not experience the quality drops. You can check the uploaded files to see this.

I agree that 320Kbps LC-AAC 5.1 is the best of the options. It sounds very good, it is still subordinate to original, but very very acceptable.

If you check the spectra, you can see a problem which can occur currently with AAC-HE 5.1 in Recode:
http://morbo.org/nero/Recode_audiobug_5.1ch.jpg

So, atm if you are concerned about quality fluctuation of 5.1 AAC-HE, wait for Ivan's fix.

Concerning clips 1 through 6 I can indeed only tell that there are no gross artifacts. I tend to like the higher bitrate versions better . But because I can't compare with the original 5.1 source I really can't properly ABX. Also, without dialogue its much more difficult for me to hear any differences. My brain is more used to judging voices (or music for that matter) than seemingly random noices buzzing around me .

Concerning 'the fullfilmencode', you mean the drop around 40-60s? This is indeed the timeframe where the second parachute opens. That's a real ugly point indeed . I should double-check my encodes I'm afraid.