Convert audio to 5.1 as in this other thread...

Special Interest Groups Audio Processing
1

Hello,

I’m a new user of this forum and Audacity. I know to use the beta software to be able to map my wavs to different channels.
Please direct me to a post if this question has already been answered.

I need help using audacity to accomplish the following:
http://forum.videohelp.com/threads/99196-2-Channel-48Khz-WAV-to-5-1-Channel-AC3?p=405834&viewfull=1#post405834

I would like to convert a stereo file into mp3 (yes, I know I won’t get 5.1 quality nor magically create the extra channel information).

For this line:

old left - old right(3dB down) + 15ms delay - 10dB = new left surround

I assume he means to bring the right channel down 3db, invert it, combine it with the old left, add a 15ms delay, then bring it down 10db

Is this correct?

Can someone explain to me what this means? Or how to do it in audacity?

old left + old right + 18dB per octive filter centered at 180Hz (crossover, your wave form will look like this “~~~~~ ___________________” )

  • 2dB @ 80Hz .7 octive wide + 3db @ 180Hz .8 octive wide

Any help appreciated!

2

<<<18dB per octive filter centered at 180Hz>>>

Cool. That’s how he got the LFE Low Frequency Effects channel from the main show. You could probably do the same thing with Effects > Low Pass Filter at 180 Hz. He was doing a very specific frequency equalization curve. Yes, you need to be able to translate the instructions to the Equalizer tools.

Koz

3

He’s not been very clear with that line, (and I’m not an expert with surround sound)
He may mean that, or he may mean:

(old left mixed with inverted old right) amplified by -3dB (minus three)
mixed with (+)
(old left with inverted old right) amplified by -10dB (minus ten) and delayed by 15 milliseconds.

Either of these interpretations will produce a kind of fake surround sound, but they will sound different. Experimentation is called for.

Combine the left and right into a mono channel (in Audacity 1.3.12 you can do this with “Stereo Track to Mono” from the “Tracks” menu).
Then apply an Equalization filter that looks something like this:
Equalization_027.png

4

Wow! Didn’t expect such great replies.

Thanks for taking the time to do this. I will come back and post my results soon so others may benefit from this. Thank you.

5

Ok. I said I’d be back and here I am.

I tried two different sets of two things.

Using the bass equalization vs the low pass filter sound almost the same and close enough for my needs. Although, I understand that the equalizer is likely more precise.

As for doing the right surround the way you suggested, or the way I thought, they both sound slightly different but I have no idea which is better. I might try just playing the surround alone to see which sounds better unless someone has a better idea to determine which to use. Either way, they both sound better than sending the same “front” sounds to the “surround” speakers.

One thing I had difficulty with was the delay in Audacity. I tried to set 15ms but the lowest I could go was .01s . As well, there were other settings such as # of echoes that I left at the default.

All things aside, this is much much better for me and my audience (maybe not for hardcore audiophiles).

6

0.01 seconds is 10ms

The default setting on Audacity’s delay for # of echoes is 5, if you only want one (“a delay”) set this to 1.
and change the “decay amount” to 10 if you want “-10db” level for the delay (default is 6).
Leave the other settings at default.

7

Hey Guys,

Thanks for the help.

I am on the route to automating this here:

https://forum.audacityteam.org/t/automating-repetitive-tasks/16838/7

Thanks again,
Billy