How to make stereo sound to 5.1?

I just noticed that Audacity can export audio with multiple channels if the format used supports multiple channels. With FFmpeg library (I don’t remember that dll’s name) I were able to export stereo AC3 files. And now I can export 5.1 AC3 files so that the left and right channels are L and R and the separated stereo/mono track (I create it using low pass filter for that track and high pass filter for the original stereo track) is the LFE channel.

But now I would like to know if it is possible to create real 5.1 sound (so that the center and surround channels produce appropriate sound) with Audacity from stereo sound? If it is possible, what plugins I would need? I know that in the normal surround / Pro Logic processing the ‘similarity’ of the front channels will be moved to the center channel and that the sounds in the front channels that have inverted phase will be moved to rear channel(s). But how to do something like that from the stereo sound in the Audacity?

So that’s 4.1 show in 5.1 speakers. The out-of phase front two are mixed down to the rear channels. There are two speakers back there, but they both have the same show.

The center mix is the one that kills you because that’s generally dialog in a movie. There is no good way to split dialog from a mixed stereo show even if the dialog is in the middle. It’s a common request.

Do you want to bother with Dial Norm?


For “real” 5.1 sound you would start with a multi-track recording. The tracks can then be “panned”, “filtered” and “delayed” to the appropriate speakers to create the desired spacial effect. If you are starting from a stereo mix, the best that you can do is to create a kind of “pseudo” (fake) 5.1 effect.
For the centre channel, mix the left and right channels to mono and reduce the bass.
For front Left/Right, try the “widen” preset in the Channel mixer plug-in.
For the rear left/right, try the channel mixer plug-in with:

New Left Channel:
Left mix = 100 %
Right mix = -100 %

New Right Channel
Left mix = -100 %
Right mix = 100 %

You could also try applying a little delay to the rear channels - insert about 40 ms of silence at the start of the track.

For the LFE channel, mix to mono and apply a low pass filter.

You will need to adjust the levels of the tracks to get it to sound right.
For the correct channel mapping, search Google, Different file formats use different channel mappings.

Thank you both for good advice!

But is there any plugin for Audacity that could separate the ‘surround sound’ encoded into stereo? I mean, the sounds in stereo track that are out of phase

What does it do? I’m not totally aware of it. Is it possible to use it when exporting with Audacity?

Dolby AC3 has sound services way over and above “put this voice over there.” Dial Norm is the setting that lets you produce thunder, gunshots and jets taking off in their real-world loudness. People producing AC3 for the first time sometimes get burned with this when the encoder they use sets it without telling anybody and nobody thinks to look.


You mean ‘wide stereo’? What about the ‘extra wide’ preset? It sounds to me that it removes most of the center information of the stereo soundstage. Would it work with mono center channel?


It depends on how wide you want it to be.
If you make it too wide, then any dialogue that has been recorded in stereo (one person to the left and one to the right) might sound weird - as if they are throwing their voices. Try both and see which you prefer.