I wanted to create a quick "fake" stereo version that sounded better than the flat-sounding mono version. The Haas Effect seems like a suitable alternative to the real thing, although obviously not as good as true stereo.
Here is how I did it with Audacity Portable version 1.3.13-beta
For this example, I am using a file called fx-mono.wav as my source.
- Open Audacity
- Drag-n-drop your mono audio file onto Audacity's window (or use File --> Open)
- Let's add a small chunk of silence at the beginning by placing your cursor at 0.0 and click Generate --> Silence --> (select hh:mm:ss + milliseconds) --> 00h 00m 00.030s (this adds 30 milliseconds to the beginning)
- Select the entire track (click-n-drag) and click Edit --> Copy (or CTRL+C)
- Click Tracks --> Add New --> Stereo Track. This will add an empty stereo track below your mono track.
- Place your cursor at 0.0 in the stereo track and click Edit --> Paste (or CTRL+V).
- There should now be identical copies of the track in the upper and lower section (left and right).
- Now to avoid confusion, go ahead and click the X button on the top-left of your mono track to close it. We don't need it anymore at this point.
- There is a drop-down on the top-left of your new stereo track which should have the name "Audio Track." Click this drop-down selection and select "Split Stereo Track."
- Now that we have each copy separated, what we do to one will not affect the other.
- In the control area on the left of the top section, move the slider marked "L" and "R" all the way to the left. This causes this chunk of audio to only come out of the left channel.
- Do the same for the bottom section except move the slider to the far right.
- If you click play at this point, you will still hear the same, identical audio sound that you started with (well, a microsecond of silence at the beginning but it should not be noticeable). However, we are now in position to implement the Haas Effect.
- Zoom into the bottom audio section so you can see the beginning where we inserted 30 milliseconds of silence.
- This is the part where you will need to play it by ear by deleting a certain amount of that silence and listening to the result. The more silence you remove, the more pronounced the effect will be.
- Select the desired amount of silence at the beginning and click Edit --> Cut (or CTRL+X) and click the play button to hear what it sounds like. Click Edit --> Undo (or CTRL+X) to go back to the way it was if you don't like it and try selecting a different amount.
- On the bottom audio section, move the "-" and "+" GAIN slider slightly to the left, let's say to -2 dB
- Now place the cursor somewhere in the bottom audio section, click Effect --> High Pass Filter --> click OK to accept the default of Rolloff 6 dB, Filter quality 0.7071, Cutoff frequency 1000.0
- See if that sounds better. If not, undo the last change you don't like.
- When you are happy with the result, click File --> Export. Type in a filename you want to use and whatever filetype format. I tend to keep them in WAV signed 16 bit PCM but you may want something else.
EDIT: If you need your audio converted...such as converting from an iPhone .m4a, just go to Media.io to have it converted online to WAV format.