If you use Wavosaur for mastering / premastering, or signal analysis in a more general way, you need tools for audio analysis : spectrum analyzers, phase analyzers, sonogram.
Wavosaur comes with analyzers, you’ll find them in the ‘tools’ menu, along with oscilloscopes & statistics about the sound file (maximum sample peak, RMS power, average value.).

• Best Spectrum Analyzer Plugin
• Winamp Spectrum Analyzer Plugin
• Spectrum Analyzer Plugin Vst Free

But you can also use VST plugins (for some people it can be more convenient).
We have searched deep deep inside deep deep down inside into the web, to find the best free VST plugins for audio analysis, here’s the selection:

IZotope Insight. IZotope’s aptly-named Insight gives you a broad overview of the spectral content of. Size 6.28 MB / 18.8 MB / 18.7 MB SPAN is a real-time fast Fourier transform audio spectrum analyzer plug-in for professional music and audio production applications. SPAN provides you with a very flexible mode system which you can use to setup your spectrum analyzer preferences. 2D / 3D Full Featured Parametric Multi Channel Spectrum Analyzer ( VST / AU and AAX ). Welcome to the world of Oscarizor Pro. Parallel waveform, spectrum & stereo field comparison in 2D and 3D using side-chaining and 255 send/receive channels (up to 10 channels parallel) is the power of Oscarizor Pro – especially the multi channel spectrum analyzer in VST / AU and AAX variants. Spectrum Analyzer is a free, Windows only, real-time spectrum analysis VST plugin. The idea was to create an old-fashioned tool reminiscent of classic hardware analyzers of the earlier centuries. Another unique (and quite experimental) feature of the plugin is its detached spectrum display window, freely resizable independently.

1) Spectrum Analysis

1.1) Voxengo SPAN

This spectrum analyzer uses FFT to display the signal frequency in real time.
You can freeze the display, and use the mouse to shows dB values / Frequency value
Frequency is displayed in Hz and in musical note.
The Voxengo SPAN analyzer also displays statistics : RMS power, and it features a clipping detection.

Free vst side change. More info and download @ http://www.voxengo.com/product/span/
It is worth mentioning these plugins too, freeware!

1.2) Mdsp SmartElectronix Fre(a)koscope

Very nice, with interesting options for the spectrum display : linear/logarithmic/semitones .
Adjustable size for the FFT buffer. Had sometimes display problem with Wavosaur.
More info and download @ http://mdsp.smartelectronix.com/freakoscope/

1.3) BlueCat FreqAnalyst

Like the previous VST effect, this one can show spectrum of left / right channel or both, has a “hold peak” feature that is interesting, when dealing with EQ level in your mix.
More info & download @ http://www.bluecataudio.com/Products/Product_FreqAnalyst/

1.4) Seven phase Spectrum Analyzer

This one is freely resizable inside the host application (works in Wavosaur)
More info and download @ http://sevenphases.wordpress.com/spectrum-analyzer/

1.5) MultiInspector free

Download @ http://www.vertexdsp.com/downloads.html#MultiInspectorFree

2) Sonogram

2.1) ag-works sonogram sg-1

This free plugin displays a scrolling sonogram for frequency analysis.
You have the choice for the sonogram colors, and many options to tweak the sonogram displays
This is the only sonogram VST we have found for free ! Fortunaly it’s very good.
More info & download @ http://ag-works.net/plugins.sg1.htm

3) Goniometer

3.1) Flux Stereo Tool

When you need to visualize your stereo position, and the repartition in the field, this plugin is very useful. You can check for phase errors in your mixes.
download @ https://www.fluxhome.com/download

3.2) Gonio3

download @ http://www.uk-music.de/index.php?page=downloads

3.3) HOFA 4U Goniometer & Korrelator

download @ http://hofa-plugins.de/pages/start_en/4u_en.php

If you think that we have forget some free VST analyzer plugin in this list, do not hesitate to comment !

Edit:

We just have found this pretty nice analyzer somewhere on our harddisk :

Dust Analyzer:

It provides three modes : spectrum / scope / phase , with “hold peak” option, freeze option, dB/Freq display with mouse, linear / logarithmic scale

more info & download @ KvR audio forum & http://www.signaldust.com/

Features Application areas Details Changelog

Oscarizor – 2D/3D Multi Channel Spectrum Analyzer Audio Plug-In VST / AU & AAX / Free & Pro

„Sugar Audio’s blindingly brilliant multichannel spectrum analyser has hit the market […] It’s as easy on the eyes as it is on the wallet.” – Computer Music Aug/2016, P.26

„It’s a great little plugin that will definitely come in handy at some point if you’re a sound designer, or if you simply want to have a better visual control over the sounds that you’re working with.” – bedroomproducersblog.com

Downloads & Purchase

2D / 3D Full Featured Parametric Multi Channel Spectrum Analyzer ( VST / AU and AAX )

Welcome to the world of Oscarizor Pro. Parallel waveform, spectrum & stereo field comparison in 2D and 3D using side-chaining and 255 send/receive channels (up to 10 channels parallel) is the power of Oscarizor Pro – especially the multi channel spectrum analyzer in VST / AU and AAX variants. Use DAW host synchronization to exacly compare waveforms. Nearly an unlimited count of instances inside your DAW projects is possible. Waveforms and spectrums are displayed with wonderful filled/lined graphics using blending, blending types, smoothing and antialiasing. Choose from common colors to beautify your dB or amplitude scaled view. Use the custom UI coloration, free resizing capabilities and innovative control multi panel to optimize your workflow. Read about the features of Oscarizor Pro.

Features

• 2D / 3D full featured parametric multi analyzer
• Multi channel waterfall spectrum analyzer audio plug-in with mountains, bars, cylinder and tube models
• Parallel waveform & spectrum comparison using side-chaining and send/receive channels
• DAW host synchronization, initial autosync to receives & resync to receives button
• Automatic instrument tuner with FFT size and function memory
• Multi channel correlation & gonio meter
• FFT size, window (7 functions) & average controls
• Spectrum tilt/slope knob & Nyquist mode
• Nearly unlimited instances in your DAW projects
• 255 channels to send/receive waveforms and spectrums to/from other instances
• 10 channels simultaneous view
• Channel naming with propagation to receiving channels
• Parallel and overlay view modes
• Combined 2D/3D views Osc/Spectrum or Osc/Spectrum/Gonio meter
• Stereo, mixed mono (avg/max) & M/S (mid/side) view
• Filled/lined waveforms using blending, blending types, smoothing and
  antialiasing
• 360 degrees three axis 3D rotation, free positioning and zooming
• Two independent 3D light sources with extended customization
• Custom UI & waveform coloration
• DB and amplitude view
• Absolute view for better analyzation
• Beat and measure display adjustment
• Reset / Bypass / Freeze / Freeze all (global freeze) buttons
• Signal modifying Gain, phase switch, L/R swap and mono controls
• Sine test tone generator
• Exact mouse wheel zoom in/out
• Free positioning, scaling & dragging
• Multipanel UI control with all-in-one-mode, menu splitter & control scrolling
• Freely resizeable GUI from very small to enormously large
• Full window and control hover mode
• Preset Manager, quick save/load presets & A/B Comparison
• SA 3D Engine 2.0: Highly optimized and customizable 3D renderer
• No dongle required (except AAX), zero latency and low cpu usage (except 3D)

Application areas

• Detailed spectrum and waterfall analyzation in mixing, mastering, djing and teaching
• Averaged spectrum comparison of received channels (e.g. reference tracks)
• Spectrum interference visualization (lightens parts with most activity)
• Stereo field, mid/side & correlation analyzation
• Compression tunings
• Limiting fine-adjustments
• Envelope shaping analyzations
• Transient control
• Ducking
• Leveling / metering

2D multi channel waterfall

Use the 2d waterfall in parallel, stereo, M/S and/or overlay mode.

3D multi channel waterfall

Use mountains, bars, cylinder or tube 3d waterfall models with 2 light sources and emissive, ambient, diffuse and specular light controls. The highly optimized and customizable SA 3D Engine 2.0 renderer supports additional parameters like model width, depth, back face culling and perspective control.

Parallel and overlay view modes & 10 channels simultaneous view

Parallel mode shows all active channels in parallel mode from top to bottom instead of showing them in overlay mode.

Best Spectrum Analyzer Plugin

3D multi channel spectrum analyzer & oscilloscope

Use a single analyzer or one of the combined views.

3D Rotation, positioning and zooming

Use the 360 degrees three axis 3d rotation, free positioning and zooming.

Compression analyzation

See exactly what your compressor effects.

Transient analyzation

See exactly how transient controllers change your signal.

Multi channel stereo spectrum analyzer

Analyze which frequencies are interferencing.

Multi channel correlation meter

Have just one look to see that everything is fine with your channel correlations.

Stereo 3D combined and overlay mode

Deactivate the grids and have an exclusive view to the signals.

Multi channel gonio meter

Make reliable judgments about your stereo image.

Channel naming & solo/hide controls

Winamp Spectrum Analyzer Plugin

Enter the channel name, choose the color and turn solo/hide on/off for every channel.

Freely Resizeable GUI from very small to enormously large

Freely resize the effect window by dragging the bottom right corner, the multi panel controls are dynamically arranged depending on the UI size.

Waveform smoothing

Smooth the waveforms from the common visualization to…

… medium smoothed or …

… maximum smoothed waveforms.

Absolute view for better analyzation

Shows the waveforms in absolute mode. Negative waveform parts are transcoded to positive parts.

Custom waveform coloration

Choose the color of all signal waveforms.

Stereo absolute view

Displays two channels (L/R) of all displayed signals instead of one mixed mono channel.

Multi stereo dB view

Displays two channels for all signals in dB mode.

Exact mouse wheel and left button zoom in/out

Use your mouse wheel or mark waveform parts to zoom in/out the display at the current mouse position.

Non filled view

Turns off the filled waveforms.

Blend types

Choose from 5 different types of graphical blending types to optimize the visualization.

Automatic instrument tuner

The chromatic and automatic instrument tuner comes in handy when you just want to quickly tune your instrument.

Custom UI coloration

Adjust independently the main, secondary, view and background RGB color values.

Full window and control hover mode for the whole 2D 3D multi channel spectrum analyzer audio plug-in VST AU AAX

Use the full window to analyze your signals.

Changelog

Spectrum Analyzer Plugin Vst Free