There are many analytical tools available for the PC (from VST analysis plugins to full audio analysis software) which can help identify such things as:

• Key, tempo and pitch
• RMS and dB levels
• Frequency spectrum (i.e. to identify a build up of frequencies in a particular band, where instruments are competing with one another, or to identify the noise floor of a recording or medium)
• Glitches (clicks and pops etc.) for later repair and noise/hiss for removal
• Differences (e.g. why one release of a track may sound different from another; i.e. identifying compression and limiting and other mastering methods that may have had a negative impact on fidelity)

APPLICATIONS

The most interesting free software that we've come across for conducting such analysis is Sonic Visualizer, developed at the Centre for Digital Music (University of London) by Chris Cannam.

In conjunction with the Vamp Plugins (for which Sonic Visualizer acts as a host application) Sonic Vizualiser can perform a wide range of analysis such as key, pitch and note detection, beat tracking, melodic range and peak frequency spectrum analysis, and much more:

Sonic Visualizer with Spectogram and Key Detetection panes (click to enlarge)

Foobar2000's ABX Comparator is an excellent listening test utility which enables the blind comparison of two audio files from within foobar2000. A very handy tool for musician's to compare various mixes of the same track. For more information on Foobar2000 and its many features click here.

VST PLUGINS

To run VST analysis plugins you'll need a VST host. We recommend Reaper or if you want something lighter then Kristal Audio Engine, though Kristal is limited to only 2 VSTs per channel.

Here's a screenshot of Reaper running 3 VST plugins (Gonio3, Sonogram SG-1 and Inspector):

Here is a list of the best free VST analysis plugins (those mentioned on the first list can be downloaded from KVR Audio's VST database):

• CTuner (C-Plugs): a guitar (and other instruments) Tuner plug-in
• Gonio3 (UK Music): a simple vector oscilloscope with correlation graph for evaluation of the stereo image of your audio signal
• FreqAnalyst (Blue Cat): a real-time spectrum analyzer with smooth response and complete control over the audio spectrum analysis. Its customizable user interface and transparency feature let you make it totally integrated in your favourite audio application: check the audio spectrum and see behind it.
• SPAN (Voxengo): a real-time FFT spectrum analyzer. For the most part it was derived from Voxengo's GlissEQ and CurveEQ professional equalizers and it reproduces their spectrum analysis functionality
• Sonogram SG-1 (ag-works): a real-time sonogram allowing for fast and detailed spectral analysis.

VST's available elsewhere:

• Inspector Free (Roger Nichols Design): a very useful metering tool for the master channel (includes: spectrum analyzer, customizable alarms for headroom, balance and clipping; Peak & RMS meters, channel balance meter, customizable meter caution and warning zones)
• QSpectrum (Concrete FX): a 128 band spectrum analyzer

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