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.).

If you’ve been producing for more than a week, I’m pretty sure you’ve heard of Serum. Does Ableton have an oscilloscope? I need a way to look at the waveform coming out of my MIDI tracks. Freeze then flatten won't meet my needs, because what are you going to do if you're using the waveform as a guide for adjusting effects, freeze and flatten a clip at every setting? That would take forever.

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:

1) Spectrum Analysis

The 20 best Compressor VST Plugins of 2020 include: FabFilter Pro-C2. Also, it has an accurate oscilloscope and can operate synced or retriggered via MIDI.

1.1) Voxengo SPAN


Best Oscilliscope Plugin Vst

Vst plugin izotope ozone 7 vst3. 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.

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/

J-Scope is a VST* oscilloscope plugin, which can prove invaluable to anyone who develops audio software and has a need to diagnose problems or visualise waveforms.

Best Oscilloscope Plugin Vst Plugins

In operation it is very similar to a real oscilloscope, and most controls will be familiar to anybody who has used a hardware 'scope. The addition of a control for phosphor decay time allows the examination of rapidly changing waveforms as well as slowly evolving sound envelopes.

J-Scope accepts a stereo signal, and can display it in several modes:

  • Two separate traces, L and R
  • Single trace, sum of L and R
  • Single trace, difference between L and R
  • X/Y (Lissajous) plot, L vs R
  • X/Y (Lissajous) plot, Sum(L+R) vs Diff(L-R)

Other features of J-Scope include:
New in V1.1

Best Oscilloscope Plugin

  • One-shot trigger mode with optional pre- or post-delay
  • Linear, logarithmic and polar graticules
  • Cursor measurement of level, time, frequency, note
V1.0
  • Timebase from 1s/div (0.1Hz) to 0.1ms/div (1kHz)
  • Gain (Y) from x0.1 to x100
  • DC or AC coupled
  • Variable X-offset of trace(s)
  • Y-offsets of stereo traces individually adjustable
  • Adjustable trigger level, on positive or negative slopes
  • Delayed triggering
  • Display 'freeze' option
  • Adjustable phosphor persistence
  • Optional graticule with variable brightness
  • 8 preset modes for quick setup

J-Scope is donation-ware, downloadable from this site only - you may not sell it, make it available through any other website, or redistribute it in any way without my express permission.

Download JScopeV1_1.zip Windows 32-bit VST 2.4 zipfile, 438KB
Download JScope_x64_V1_1.zip Windows 64-bit VST 2.4 zipfile, 462KB

To install, simply extract the file jscope.dll or jscope_x64.dll and copy it to your VST directory.
If you find J-Scope useful, you might like to buy me a virtual beer by making a small donation.
Cheers!

J-Scope was developed using the excellent Skinman and Knobman GUI tools from g200kg.

Disclaimer: J-Scope is believed to function as described above and is offered in good faith on an as-is basis. However, you use it at your own risk - I cannot accept responsibility for any loss or damage caused by the installation or use of this software.
J-Scope is currently available as a 32-bit or 64-bit Windows VST 2.4 plugin.