Noise in AC3 encoded files

[King_Diamond]

I am having problems when I encode an avi file to ac3. There are noises at certain instances, noise like the "popcorn" heard in old LPs. This is more evident when I encode a 5.1 channel. Does anyone know what it can be?

Btw the avi file has no noise and I use the default settings of the ac3 encoder as I am no expert in such options.

[KpeX]

Please describe your playback chain (software & operating system used, audio-out type (analog or SPDIF), cables used, speakers/amplifiers used (computer speakers, TV, home theater system) ). Also please specify what sample rate your source material is, whether or no you're resampling, and what encoder you are using. Remeber we can't read your mind.

[King_Diamond]

Sorry but I am quite new to this.

Software - Premiere Pro AC3 encoder (Minnetonka)
OS - Windows XP
Audio-Out type - Analogue
Cables - RCA phonos Video, Audio Left, Audio Right
Speakers/amplifiers - PC speakers and home theater system
Rate - 448
Dont know what you mean with resampling, can you please explain?

Hope this is ok but if more info is required, please ask.

Thanks.

[Mug Funky]

resampling is turning one sample rate (like that of CDs, 44100 hz) to another (like that of DVDs, typically 48000 hz).

if it's done badly (if premiere does it...) then it'll give a crunchy sound referred to as aliasing. it's analogous to resizing an image by nearest-neighbor. a good resampler will do much nicer things to the audio (though you may still hear a difference if you've got good equipment, great ears and know what to listen for).

if your source is DV, then there's probably no resampling going on. however, premiere pro is the stuff of nightmares, and any ease of use and smooth function experienced is purely coincidental. i wouldn't be surprised if it's just not decoding the audio properly. if this is the case, you can use virtualdub to rip the audio stream out of the avi, so you can treat it in a program that works a little smoother (i'm not making fun - i just had to do a huge amount of tedious editing in premiere pro, and it got in my way at EVERY stage. you couldn't intentionally write a program so bad... i hate adobe SO MUCH right now :o ).

[King_Diamond]

Sorry, source material rate is 441 (Audio CD).

[King_Diamond]

So yes, I am resampling cause the output is for dvd.

It is not a crunchy sound all the way, it happens only at peak levels, like high pitch and low frequencies. I would appreciate a good sound as you are describing, but this does not pass for me, its horrible at certain instances. Even someone who is not into good sound wouldn't like this.

I don't know your experience with premiere but I didn't have any problems, until now and this is only as regards audio (don't know if you are refering to audio and video).

I believe that it's as you said, that is, not encoding properly. However I did not change any of the default settings as I am unaware of what they are, but maybe, that would do the trick.

You suggested to rip the audio stream and use a better program. Can you explain why I need to rip the audio stream and what program would you suggest that "works a little smoother"?

[King_Diamond]

I just tried exporting as a wav file and it's fine. So I am assuming that I have the settings configured wrongly. These are the settings I am using.

Codec : Surcode for Dolby Digital
Audio Coding Mode : 5.1 Surround
Sampling Rate : 48kHz
Data Rate : 448kb/s (Don't know if this is correct)
Bitstream Mode : Complete Main (CM)
Dialog Normalization : -27
Dynamic Compression Preset : Film Standard
Center Downmix Level : -3db
Surround Downmix Level : -3db

As advanced options I have checked : Channel Bandwith Lowpass Filter and DC Filter.

Any suggestions whether I am doing something wrong?

[King_Diamond]

I believe that I found the problem but I hope that I am wrong cause it will take a lot of time to re do all. It seems that the noise is achieved when the source files exceed 0db.

I was exporting the master file to ac3 which seems to take the source files into consideration. When I exported the file as 5.1 wave and then encoded to ac3, the noise wasn't there. So the question is, does ac3 files have to be below 0db?

[Erupter]

I believe that I found the problem but I hope that I am wrong cause it will take a lot of time to re do all. It seems that the noise is achieved when the source files exceed 0db.

I was exporting the master file to ac3 which seems to take the source files into consideration. When I exported the file as 5.1 wave and then encoded to ac3, the noise wasn't there. So the question is, does ac3 files have to be below 0db?

Theoretically nothing can be over 0dB.
Because 0dB should be the maximum available line level of the signal coming out from the DAC.
Going over 0Db would cause distortion (clipping to be precise) as the DAC itself is capable of delivering a level of power defined as 0dB: if you ask more and don't have spare, clipping occurs.

[King_Diamond]

So I believe that I have to redo all under 0db right?

[Erupter]

So I believe that I have to redo all under 0db right?

I think so.

[King_Diamond]

Thanks for your help. Already started.