Soundtoys Sie-Q EQ Plug-in Analysis

Soundtoys Sie-Q EQ

Sie-Q is Soundtoys’ take on a classic German EQ from the 60s, the Siemens w295b. This EQ module from the Siemens Sitral consoles features a discrete silicon transistor design and simple controls.

Smooth and tight drive
Gentle and musical equaliser

To analyse the non-linear behaviours of Sie-Q, I ran a 100 Hz sine wave through the plug-in at various settings.

100 Hz sine wave -12 dB passed through Sie-Q at Unity

The Sie-Q generates strong low order even and odd harmonic components. Interestingly, the second, third and forth are at relatively equal levels; these harmonics produce the octave, the octave and the fifth and the second octave to the fundamental - very musical indeed!

100 Hz sine wave -12 dB passed through Sie-Q with Drive set to 9

When Drive is at 9, Sie-Q produces stronger low order harmonics and generates more high ordered harmonics. At this setting Sie-Q remains very musical but has a little extra bite.

100 Hz sine wave -12 dB passed through Sie-Q with Drive set to 15

When Drive is set to 15 the third harmonic almost equals the fundamental and the unit is in feedback, which generates a lot of higher ordered harmonics far beyond the spectrum. This setting sounds very crunchy, aggressive and sustained.

Note: Do not worry about that huge sub frequency build-up. It is DC offset and is only depicted like that due to FFT spectrum analysers not being very good at representing frequncies at 1 Hz. A simple 6dB low cut at 20 Hz will remove the DC offset, as this will reduce headroom.

For this test I ran a synth loop through Sie-Q at various settings. I have compensated for level so that the synth loop peaks at -1 dBFS for maximum resolution of the waveform in Pro-L.

Dry Synth Loop

Sie-Q at Unity

Sie-Q Drive 9

Sie-Q Drive 15

I REALLY like the saturation characteristics of this plug-in, and I strongly recommend trying it out for yourself.
At Unity the Sie-Q has a smooth and gentle soft clip behaviour, similar to the Pultec actually.
At Drive 9 Sie-Q also has smooth soft clip characteristics but look how much the average level has increased! This is my favourite setting on the synth loop below.
At Drive 15 Sie-Q breaks up and sounds very crunchy, I don’t normally like extreme distortion like this but I think it breaks up quite nicely, and look at the average level again!

Dry Synth Loop
Sie-Q Dry.aif (1.3 MB)

Sie-Q at Unity
Sie-Q Unity.aif (1.3 MB)

Sie-Q at Drive 9
Sie-Q Drive 9.aif (1.3 MB)

Sie-Q at Drive 15
Sie-Q Drive 15.aif (1.3 MB)

The EQ section is nothing spectacular in my opinion, it does have a smooth and tight sound, though.

White noise passed through Sie-Q Low/High Shelfs at Max Boost

Low shelf returns to unity at 200 Hz and High shelf returns to unity at 2 KHz, this is not proportional/gain dependant.

White noise passed through Sie-Q Low/High Shelfs at Max Dip

The dips are proportional, less gain equal less bandwidth, very smooth sounding actually, I like.

The Mid band is also proportional ao pointless attaching a screenshot, this band also sounds nice!

Sorry Sie-Q does not instantiate properly in Mixbus, so I am unable to analyse frequency and phase response adequately.


hey paul! wow another great analysis from you. question: the dc offset accumulation here really stood out to me. are there other eq’s around that do anything similar?

Nothing like that, quite a few of the models do but its normally -100 to 110 dB for a -12 source.