SoundSoap is pretty easy to use: solo the track you’ve got selected and find a place where that person doesn’t talk. Then click Learn Noise in SoundSoap and Play (or the spacebar) in GarageBand. SoundSoap will listen to that audio, learn the ambient sound of the audio track, and automatically remove it. If the track has an electrical hum (often due to electrical interference), you can remove that too by clicking on the 50Hz or 60Hz buttons.
You can get a decent amount of noise-gating features—which silence tracks when there’s no noise above a certain volume—from GarageBand itself. In the Edit tab on the right side of the screen where you’ve been working, the top effect is Noise Gate, and it’s off by default. Click on the left side of its rectangle to turn it on, then experiment with using the slider to suppress extraneous noises from the room without swallowing your speaker when he or she is actually talking.
Depending on your preference, you might also want to compress the vocals a bit. I will often use the Compressor plug-in, set to Vocal Compression Basic, to smooth out differences in the loudness of the various recording setups of my fellow podcast panelists.
Of course, every recording setup is unique, so you’ll need to repeat this step for every audio track. Hey, I said it would make your podcast sound good—I didn’t say it would be easy.
Moving things around
The number one reason to have your participants record their ends of the conversation is because the recording will be of much higher quality than a Skype track. But a close second is this: once you’ve got everyone on their own audio track, you can actually edit the conversation to make it flow better.
Now, this is an even more time-consuming process than applying noise reduction. I’ll be honest: you could spend 20 hours editing a one-hour podcast if you tried. I don’t do that, but I do try to help my podcast conversations along by editing out interruptions, false starts, extraneous bits, and a whole lot of over-talking that happens when five people all try to talk at once on Skype. To save time, I rarely edit anything when a single person is talking (other than removing an occasional telephone ring, meowing cat, or heavy breathing from a panelist with allergies). Instead, I pay attention to each track’s waveforms in GarageBand and usually intervene only when several people are trying to talk at once.
The easiest cuts are the false-starts and failed interruptions: I just use the Edit-> Split command in GarageBand to shop up the track and delete those bits as if they never existed.
For more complicated stuff, I will actually slide parts of the conversation around. This is tricky, since you have to move all your tracks carefully or risk getting them out of sync. Generally my edits of this kind happen when several people are all saying something valid, but it all overlaps. I use the Split command to chop the key parts up. For the track I’m leaving in place, I will split the clip after they’re finished talking. For the tracks I’m moving, I’ll split them all before they start talking. Then I can select all the tracks after the splits I’ve made and pull the conversation apart.
This is kind of hard to visualize, so I made a video of this process in action, using three different speakers who all say things that overlap. In the video, you’ll see me split the conversation into pieces and drag it apart, all the while being careful to select all the tracks on the right side of the screen so that I don’t lose sync.
There are lots of advanced tricks to use here to make edits seem more natural. GarageBand lets you adjust the size of a particular clip by holding your cursor over the edge of a clip until it looks like a strange bracketed arrow, then clicking and dragging the clip left or right. This can be useful in having one person’s last word trail off while the next person starts talking, even if those two events occurred several seconds (or minutes, if you’re removing a long digression) later. Like I said, you can do this forever—if you’ve got the time. I only tend to use these techniques in order to make necessary edits sound more natural.
Exporting and the rest
When you’re done editing, zoom out in GarageBand and eyeball your timelines. I’ve had a couple of occasions where I made edits to tracks where more than one segment was highlighted by accident, which resulted in huge sections of track being moved to the wrong place. When I looked over the timeline, I saw the empty space and was able to fix it before sending it out.
When I’m done editing a podcast, I generally export it as an uncompressed AIFF (to do this, you must hide the podcast track if it’s visible (Track -> Hide Podcast Track), then choose Share -> Export Song to Disk… and export the song to disk “in CD quality” by making sure Compress is not checked. Then I drag and drop the file onto the excellent free Levelator utility, drag the output file into iTunes, and use iTunes to encode the podcasts. If you don’t want to use the Levelator to manage the loudness of your podcast, it’s even easier: just use GarageBand’s built-in encoding settings. I tend to use 56kbps or 48kpbs mono, but what you choose depends on how much you care about sound quality and how much bandwidth you’re willing to pay for.
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