lowpass filter when encoding ac3

[ddawes]

Morning,
Downmixing 6ch wav to 5.1 ac3 using BeSweet. Is there a CLI switch that I may use to control whatever the preset freq is for the lowpass filter to LFE? I would like to remove bass from all other channels and send directly to LFE. I can set that from the BeSweet GUI "Azid 1" settings page, correct, by checking "LFE to LFE output" box? Am I not seeing an option to adjust that freq, somewhere? Also, since I am selecting LFEto LFE in the DOWNMIX LEVELS area , in the OUTPUT MODES area, should I select DECODE(Front/Rear) 3/2? I know that LAME has --lowpass switch. Can that work with Azid as well?

Thank You.

[Skelsgard]

Downmixing 6ch wav to 5.1 ac3 using BeSweet.
1) If your source has the same channel number than your output, then you´re not downmixing nor upmixing (6ch --> 5.1, where 5+1=6).
2) Don´t use BeSweet for AC3 encoding, its ac3enc.dll is a low quality encoder.

Is there a CLI switch that I may use to control whatever the preset freq is for the lowpass filter to LFE?
No, at least not in any encoder at this moment.
Lowpass filters for LFE in AC3 are about 120 Hz (should ask what frequencies Aften developers are using for lowpass), though Vegas, in its project settings has an option for setting the lowpass to use with the LFE channel , and offers 4 choices:
- 80 (Dolby consumer/DVD)
- 116 (DTS)
- 120 (Dolby pro/film)
- 180

I would like to remove bass from all other channels and send directly to LFE. I can set that from the BeSweet GUI "Azid 1" settings page, correct, by checking "LFE to LFE output" box?
Nop, that setting is not for that.
LFE to LFE Output controls the gain the LFE channel will have if directed to the LFE output(as in no downmixing of the LFE into other channels is being done). 0 gain (no gain) means the LFE will go untouched to the LFE output of the output file.
If you want to send the low frequencies from all the channels to the LFE, you´ll need an advanced audio editor with some frequency filtering capabilities.

Also, since I am selecting LFEto LFE in the DOWNMIX LEVELS area , in the OUTPUT MODES area, should I select DECODE(Front/Rear) 3/2?
You don't need azid in your command line as you´re encoding to ac3 with besweet, which uses the -ac3enc() command, and azid is an AC3 decoder.
BeSweet.exe -core( -input 6ch.wav -output 6ch.ac3 -logfile BeSweet.log ) -ac3enc( -b 448 -6ch )

I know that LAME has --lowpass switch. Can that work with Azid as well?
Azid doesn' have a lowpass filter like the one you need.

Cheers

[ursamtl]

I would like to remove bass from all other channels and send directly to LFE.

Just remember that if you do remove frequencies and send them only to the LFE, and then use the file to create a DVD or surround CD, these frequencies will be completely lost for playback on Dolby Pro Logic systems, as the LFE data is discarded.

[ddawes]

Thank you very much indeed for the helpful info. You've helped me make better sense out of what I'm doing, and that says alot, lol.