I am not sure if anyone else has to manage audio files that have been .mp3 encoded prior to editing but for the podcast it has been causing some issues. This week however, I made a few changes to the encoding and it appears to have made a significant difference. Here is what I have done and if anyone has any further suggestions I would appreciate it.
The background of this whole saga is that I used to record the podcast using Hot Recorder. Since the release of Skype 3.0+ this has failed to record anything but silence. Although he website claims it does work with 3.0. So we had to look to an alternative. Knightwise has a Mac so that made it a lot easier for us to decide what to do but our decision then presented a few things we had to work around.
For some reason recording Skype on a Mac is relatively easy compared to a Windows based machine. Not sure why. It might be the way that Mac handles audio or that there has been more development on the Mac in this regard. So we decided to record the show on Knightwise’s Mac. He uses Call Recorder to record Skype, which by the way has excellent results. Far superior to what I was getting with Hot Recorder. But now we had a great recording of the show in .wav which is generally about
1GB in size… +2.4GB but it was on the other side of the world! We needed to get it to Oz in one piece and in good enough quality to work with.
A great supporter of the podcast donated a server which has excellent speed and storage in addition to as many FTP accounts as we needed. However sending a 1GB file across the world is out of the question, even zipped up it would be huge! The only answer that we could see was to encode the .wav as an .mp3 in as high a quality as possible. So Knightwise encodes the file raw as a 192 kbps, CD quality. The result is about 100MB, which is very manageable. He then sends the file to me via FTP.
I download the file and convert it to a .wav and edit the show as per usual. When finished the file would be encoded as an .mp3 at 64 kbps at 44100 khz. We dropped the bps a while back to give us a smaller file size, which we thought would be appreciated. However since we swapped to Knightwise recording the show the 64 bit quality has been giving us poor results. I have tried to optimize for quality in the encode but it has made no difference.
The problem is that .wav files loose certain frequencies when they are encoded to .mp3. You can’t get them back they are gone forever. Sure I do everything that I can to get the best results. But the 64 bit rate was stripping more of those frequencies out of the final file than I would like. This resulted in some rather strange sounding ambient sounds and hissing when there was talking in addition to making the music tracks terrible. There was only one thing for it.
This week I increased the bit rate. Although in the beginning the show was encoded at 96 kpbs; I thought I would take the intermediate step of 80 kpbs. The result was a file that was only about 4-5 MB larger but the pay off in quality I think was worth it.
The conclusion is that when we changed the way the show is recorded and then encoded before transfer, we should have decided to increase the bit rate. The 16 bit increase in quality has compensated for the lost frequencies the first time it was encoded as an .mp3 making the file resilient to being decoded to .wav and then back to a .mp3. A few further tweaks at the recording end will give us some further head room as far as quality.
I would remind all podcasters out there of one of the golden rules of editing, never edit a .mp3, always convert it to a .wav. I hope this hack helps anyone else faced with the same problem of transcontinental podcasting and file transfer. Check out this weeks show and compare the difference.
UPDATE: Hot Recorder has been updated to version 2.14, which I am told does work with Skype 3.0+. I am yet to test it but I will let you know the results. Thanks to mswiczar for the tip in the comments.