Soundtoys Radiator Plug-in Analysis

#1

SOUNDTOYS RADIATOR

RADIATOR OVERVIEW
Radiator was designed for adding warmth and grit; turning up the HEAT on your mixes. Radiator is based on the Altec 1567A, the original hardware, introduced in the early 1960s, which was a rack-mounted five-input tube mixer. It featured removable transformers, a simple two-knob EQ, and a whopping 97 dB of gain!

RADIATOR CHARACTERISTICS

  • Tube and transformer topology
  • Big, smooth, warm and punchy
  • Gritty and noisy
  • Brings tracks to life

SIGNAL FLOW
The input signal is fed into the first tube saturation stage with the drive level determined by the input control. The signal then flows into a 2-band EQ section with Bass and Treble controls. After the tone controls, the signal reaches the second saturation stage. This is controlled by the Output knob. Finally, the processed signal is fed into the Wet/Dry mixer.

RADIATOR CONTROLS

Input
The Input control determines the amount of drive into the first tube saturation stage.

Mic/Line Switch
The Altec 1567A has a very impedance dependent response in regards to the input. The Mic and Line modes represent the differences in behaviour observed with a 150ohm impedance (Mic) vs. 600ohm (Line) signal.

Noise Switch
The 1567A has a significant amount of circuit noise even at low saturation levels, and this noise was modelled and included in Radiator. It averages -68dBu at the maximum measured settings, and is reduced by 10dB with the “Line” source selected.

Radiator Line Circuit at Unity with Noise Engaged


Radiator Mic Circuit at Unity with Noise Engaged

Noise is quite audible, I generally use Radiator in clean mode but if you want a bit of noise perhaps consider plug-in order, and insert Radiator post compression.

Tone Controls
Both the Bass and Treble controls allow for a +/-10dB boost/cut. The frequency response behaviour mirrors that of the original 1567A with a wide curve for bass frequency cut and more of a sloping boost.

Radiator Bass EQ Curves
Radiator-Tone-Bass
Radiator Treble EQ Curves
Radiator-Tone-Treble

Output
Output determines the level of post-tone audio entering the second stage of saturation before being fed into the wet/dry mix. This means that, true to the original unit, additional saturation of the signal can be achieved through boosting the output.

HARMONIC ANALYSIS
To analyse the non-linear behaviours of Radiator, I ran a 100 Hz sine wave through the plug-in at various settings. In addition, I passed Radiator through a Hammerstein module and a 2D Spectrogram to trace the amplitude of the harmonics across the frequency range of the plug-in.

100 Hz sine wave at -12 dB passed through Radiator’s Line Circuit at Unity


100 Hz sine wave at -12 dB passed through Radiator’s Line Circuit +6dB Input -6dB Output

100 Hz sine wave at -12 dB passed through Radiator’s Line Circuit -6dB Input +6dB Output

100 Hz sine wave at -12 dB passed through Radiator’s Mic Circuit at Unity

100 Hz sine wave at -12 dB passed through Radiator’s Mic Circuit +6dB Input -6dB Output

100 Hz sine wave at -12 dB passed through Radiator’s Mic Circuit -6dB Input +6dB Output

Radiator generates strong low-ordered, even and odd harmonics in both Line and Mic modes. The second harmonic adds body and is often associated with a warm and smooth sound. The third harmonic tends to sound fat and is associated with richness and depth.
The Line circuit generates more higher ordered harmonics when compared to the Mic circuit. Higher ordered harmonics, especially above the seventh are particularly dissonant, and give a sound edge or bite, often with a sharp attack quality.

Radiator Line Circuit at Unity passed through a Hammerstein module (4 Orders)


Radiator Mic Circuit at Unity passed through a Hammerstein module (4 Orders)

Radiator Line Circuit at Unity passed through a 2D Spectrogram


Radiator Mic Circuit passed through a 2D Spectrogram

It is interesting to see how the individual harmonics are affecting the sound. I only plotted the first 4 harmonics on the Hammerstein module, as the graph gets a little convoluted when depicting additional harmonics.
Explanation : The Hammerstein module plots a trace per harmonic. The trace amplitude depicts the amplitude of the harmonic across the frequency range of the plug-in.

SOFT CLIPPING CHARACTERISTICS
For this test I ran a drum loop through Radiator at various settings. I have compensated for level so that the drum loop peaks at -1 dBFS for maximum resolution of the waveform in Pro-L. In addition, I passed a sine wave through Radiator at various settings and captured the results on an oscilloscope.

Drums – Radiator Disabled


Drums passed through Radiator’s Line Circuit at Unity

Drums passed through Radiator’s Line Circuit +6dB Input -6dB Output

Drums passed through Radiator’s Line Circuit -6dB Input +6dB Output

Drums passed through Radiator’s Mic Circuit at Unity

Drums passed through Radiator’s Mic Circuit +6dB Input -6dB Output

Drums passed through Radiator’s Mic Circuit -6dB Input +6dB Output

Very subtle soft clipping behaviour that sounds smooth! It is interesting on the Line circuit that amplitude drops a little when kick and snare hit together.

Oscilloscope – Line circuit at Unity


Smooth soft clipping behaviour on the positive portion of the waveform, more squared on the negative portion.

Oscilloscope – Line circuit with I/O at +15dB


Both positive and negative portions of the waveform are now more squared. This will generate more odd ordered harmonics. Interestingly, the duty-cycle of the negative portion of the waveform has been elongated, which generates even ordered harmonics.

Oscilloscope – Line circuit with I/O at +15dB, Wet/Dry at 90%


I found adjusting the Wet/Dry control by only a few percent was very good for rounding out the clipping behaviour.

Oscilloscope – Mic circuit at Unity


Oscilloscope – Mic circuit with I/O at +15dB

Oscilloscope – Mic circuit with I/O at +15dB, Wet/Dry at 80%

Radiator has asymmetrical soft-clipping behaviour.
Asymmetrical clipping saturates either the positive or negative portion of the waveform more then the other. This causes the generation of both even and odd ordered harmonics,

FREQUENCY AND PHASE RESPONSE
Frequency and phase response of Radiator at unity and then how particular settings change this relationship.

Frequency Response of Line Circuit at Unity


Line sounds ‘phat’; the frequency response demonstrates why, look at that sub frequency bump.

Frequency Response of Line Circuit +6dB Input -6dB Output


Frequency Response of Line Circuit -6dB Input +6dB Output

Frequency Response of Mic Circuit at Unity

Mic always sounded ‘thinner’ than Line, there is a significant attenuation in the bass region and a sharp cut off from around 10KHz.

Frequency Response of Mic Circuit +6dB Input -6dB Output


Frequency Response of Mic Circuit -6dB Input +6dB Output

Phase Response of Line Circuit at Unity


Perhaps be careful when utilising Radiator as a parallel effect on very low frequency instruments. Although I think this is too low to have any audible effect.

Phase Response of Line Circuit +6dB Input -6dB Output


Phase Response of Line Circuit -6dB Input +6dB Output

Phase Response of Mic Circuit at Unity

Phase Response of Mic Circuit +6dB Input -6dB Output

Phase Response of Mic Circuit -6dB Input +6dB Output

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Soundtoys Little Radiator Plug-in Analysis
#2

Brilliant job, @Paul! Very informative.