Learning to Podcast: Audio Wrangling

written by Geoff Bowers on Saturday, 28 January, 2006 @ 12:00 AM

Trying my hand at a bit of podcasting.. its surprisingly more involved than I first imagined. Thought I might share the trials and tribulations for those who want to try their hand at this malarky. First I had to wrestle the audio into shape.

Recording Audio

Although I've done a fair few Breezo's and the like I'm not really trying to record my own show just at the moment. I've got tens of hours of audio tapes from the sessions of the last two webDU conferences so I begin with a bunch of randomly labelled casettes. This means I don't have the luxury of sorting out a decent mike and re-recording bits that have gone wrong.

Would you believe we don't have a single tape player left in the house? So after months of procrastination I finally get round to shopping for a tape deck. Basically I hate shopping. So when I tell you I went to four different electronics stores you can bet it wasn't for kicks. Tape decks clearly don't sell well these days, and I finally had to settle for an $80 buck sony tape deck (bear in mind you can get a DVD player for $50 at the local super market). Ok -- so it's a Sony and they sold me on key features like auto-stop and a retractable handle.

I stumbled across this great piece of open source software called Audacity. It's not going to win awards for usability but its cheap, and does the trick for me. A couple of dinky cables later and I'm in business converting from analogue to digital.

Audacity Screenshot

A session on these tapes is about 50-60 minutes and the audio-visual guys seem to just flip them over when they finish a side. So once I get one of these tapes transferred I have to clean up the gaps, blips and other noises. There's an odd background noise in the background, which I can take out using the Noise Removal effect. I add a little bit of music to a second track and cross fade them together. Someone better bloody enjoy this stuff I'm thinking.

Exporting to MP3

Next you'll want to export to MP3. If you're using Audacity, you'll need to hook up the LAME encoder. The hard part for me was trying to work out what sampling rate to use. Typically I like to rip MP3's at the highest possible rate for the best quality but it makes for very hefty downloads. So I experimented.

~60 minutes of audio is about 615Mb raw and roughly translates to MP3 with the following file sizes at different bit rates:

  • 128kbs 56Mb
  • 96kbs 42Mb
  • 64kbs 28Mb
  • 32kbs 14Mb

Changing the bit rate of your export in Audacity can be achieved by opening file > preferences > file formats and selecting from a list of choices. A mono-track of someone talking at a podium mike has a lot of crap in it to begin with and you'd be surprised how good it sounds even at 32kbs. So I settled for 32kbs.

Flash Sound

Another thing I wanted to have a crack at was providing the audio directly off the web site through a Flash audio player. This is something I learnt about a little bit later in the piece but important to mention it now. You see Flash will only play audio correctly at certain bit rates. If you choose something other than a supported rate you get a kind of chipmunk effect. Supported sampling rates include:

  • 128
  • 44.1
  • 32
  • 24
  • 22.05
  • 16
  • 12
  • 11.025
  • 8

Here's a golden oldie of a tutorial on Flash Sound from 1999.

Please note, there's no doubt I've buggered up the definitions of sampling rate and bit rate and so on. But hey, like I said I'm new to these party tricks. In any event 32 seems to be my magic number -- works in Flash without squeaking and gives me a decent sound quality with a reasonable file size for download.



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