Purpose

To record audio from Skype using different applications to find the best audio output.  The expected "best" audio output will be clear and have the same sound level across all conversations in the recording.

Method

Downloaded and installed the applications from the Internet onto an iMAC with OSX 10.6.8
There were many small steps to achieve audio output that are not included in this discussion.
The automated "Skype test call" service was used as the guest.  The guest also recorded and played back audio, thereby providing a unique opportunity to hear the same voice from host and guest perspectives.

Observations

The following audio clips provide sample output from the applications listed on the MAC Skype Podcasting Toolkit webpage.  Please note that the software discussed in this article is not an endorsement.  (Clarification: Skype host is the caller and the contact is called the guest)

1 a) Skype with Audacity - LineIn - Soundflower

There is a difference in sound level between the host and guest speakers.  The host voice level is much lower than the Skype test call voice (guest).  Configuration requires more time to enabling the correct settings for LineIn and Soundflower; both need to be started before  launching Audacity and Skype.

1 b) Skype with Audacity - LineIn - Soundflower and Levelator

Same voice recording as 1a except post-processing using the Levelator.  There is very little difference in sound level between the host and guest speakers.  The host voice level is at the same level as the Skype test call voice (guest).  There is a distinctive "hollow" tin sound generated from the routing applications (LineIn + Soundflower) that can be heard from the host voice.

2 a) Skype and Call Recorder

New voice recording using a slightly different script from 1a,b.  There is a difference in sound level between the host and guest speakers.  The host voice level is much lower than the Skype test call voice (guest). The guest replayed a recording of the host at a higher level than the original host voice level.  There was no "hollow" tin sound, that was found in the routing applications (LineIn + Soundflower).  Setup was extremely easy and fast.

2 b) Skype and Call Recorder with Levelator

Same voice recording as 2a except post-processing using the Levelator.  There is very little difference in sound level between the host and guest speakers.  The host voice level is at the same level as the Skype test call voice (guest). The voices are clear and clean.

Conclusions

The workflow with the best audio output was Skype with the Call Recorder plugin (2a), followed with post processing from the Levelator (2b).  Although the Call Recorder is commercialware, it saves time and effort for a low cost when compared to the free option of using Audacity and audio routers (1a,b).

The waveforms of 1 and 2 are different because the conversation was slightly different.  Therefore comparison can only be made between waveforms with or without the Levelator post-processing.  In 1 a) and 1 b) there is a visible and audible difference that illustrates the importance of the Levelator in balancing the host and guest sound levels.  The waveform in 2a) displays similar high and low sounds, with 2b) audio leveled.

In addition, Call Recorder has the advantage of capturing video.  It is noteworthy that Audacity is useful in all workflows as an audio editor for a complete podcast with beginning and ending audio segments.  Further details on methodology can be found in the tutorials on the MAC Skype Podcasting Toolkit webpage.

An enhanced waveform comparison would require the same voice recording simultaneously via different applications.  Audacity could be used to display the waveform (db), spectrum, and pitch.  Sonic Visualiser is also useful for viewing and analysing audio.  Audio and visual perceptions would need to be calibrated with a standard tone.

The major differences between the commercialware and freeware were the convenience of setup and quality of sound.  The commercialware audio output sounded better than the freeware.  However, I'll let you be the judge, by clicking the links above to hear the sample clips.

References

Audacity: Free Audio Editor and Recorder. (n.d.). Audacity. software, . Retrieved July 12, 2011, from http://audacity.sourceforge.net/

Call Recorder for Skype - The Skype Audio/Video Call Recording Solution for Mac - Ecamm Network. (2011). camm Network. software, . Retrieved July 12, 2011, from http://www.ecamm.com/mac/callrecorder

Chris Cannam, Christian Landone, and Mark Sandler. (2011). Sonic Visualiser: An Open Source Application for Viewing, Analysing, and Annotating Music Audio Files. Sonic Visualiser. software, . Retrieved July 13, 2011, from http://www.sonicvisualiser.org

Free Skype calls and cheap calls to phones - Skype. (2011). Skype. software, . Retrieved July 12, 2011, from http://www.skype.com/intl/en-us/welcomeback/

Rogue Amoeba | Freebies: Free Software for Mac OS X. (2011). Rogue Amoeba. software, . Retrieved July 12, 2011, from http://www.rogueamoeba.com/freebies

Soundflower - Soundflower system extension for interapplication audio routing. - Google Project Hosting. (2011). Google Project Hosting. software, . Retrieved July 12, 2011, from http://code.google.com/p/soundflower/

The Levelator® from The Conversations Network. (2011). The Conversations Network. non-profit podcast network, . Retrieved July 12, 2011, from http://www.conversationsnetwork.org/levelator

The Levelator® Loudness Calculations. (2011). The Conversations Network. non-profit podcast network, . Retrieved July 12, 2011, from http://www.conversationsnetwork.org/levelatorAlgorithm