Leapwing Stage One versus Izotope Ozone Imager
Leapwing State One 2
Izotope Ozone 11 Imager
INTRODUCTION
Both of these stereo widening plug-ins are utilised at the school, are versatile with user-friendly GUIs, and have a smooth and transparent sound. However, are there particular applications where one should be used over the other?
CROSSOVER FILTER BANDS
Stage One does not offer an option to change crossover type; however, the filter will be either dynamic or linear-phase, as no phase shift relating to crossovers was detected at any setting. These filters are smooth and transparent, and I do not miss the ability to change crossover types.
Izotope Ozone 11 Limiter offers three options for Crossover filters: Analog, Hybrid, and Digital (linear-phase). I have not found a use for Analog mode, and I do not recommend it for most applications due to frequency and phase distortion, even at unity (no processing).
Analog Mode Crossover Phase Response
The above image illustrates 180-degree phase shifts at the crossover frequencies; this means the Analog Mode filters are 4-pole, 24 dB per octave filters. This could cause significant phase distortion depending on whether the processed track has phase-coherent counterparts, for instance, parallel channels, widening the snare top recording but not the bottom, etc.
Analog Mode Crossover Frequency Response
I was surprised to see a frequency shift in the signal when there was no processing; this only occurs with the Analog Mode. An investigation determined that this is a consequence of crossover band interaction; in the above case, 4 kHz and 12 kHz.
For most applications, I recommend Hybrid Mode; in my testing, I have not experienced any phase. Issues that could impact phase-coherent signals.
Hybrid and Digital Mode Crossover Impulse Response
Neither filter demonstrates pre-ringing artefacts, although Digital Mode has more latency; nevertheless, the DAW will compensate for this.
Ozone Imager provides three crossover filters and, therefore, four independent bands for processing, and Stage One offers two crossover filters for three bands of independent processing. If four processing bands are required, then the Ozone Imager is recommended. Otherwise, they are both excellent options based on the sound quality of these filters.
MONO SPREAD AND STEROIZE
Both plug-ins utilise an anti-phase algorithm that spreads frequency energy between the channels with no or limited phase distortion when collapsed to mono. This processor can be used on both mono and stereo sources.
Stage One Mono Spread 25 Frequency Response
Stage One Mono Spread 50 Frequency Response
Stage One Mono Spread 100 Frequency Response
The above images illustrate the Mono Spread parameter, which increases the magnitude of the frequency energy difference between the channels; however, it does not change the density (or delay time if thinking in terms of a typical Haas effect).
Nevertheless, this widening effect is very smooth and transparent; it does not sound “imparted” or cause a loss of spatial coherence, which can often happen in these types of plug-ins.
Ozone Imager Stereoize Setting I 25 2ms Frequency Response
Ozone Imager Stereoize Setting I 25 6ms Frequency Response
The Ozone Imager Setting I frequency contour resembles an inter-channel inverse comb filter. The delay setting changes the density of filter bands, the same as in the traditional Hass effect.
Comb Filter 2 ms Left Channel Frequency Response
For illustration purposes only, here is the frequency response of a wideband signal with a 2-millisecond delay on the left channel, and then collapsed to mono.
Ozone Imager Stereoize Setting II 25 2ms Frequency Response
Ozone Imager Stereoize Setting II 25 6ms Frequency Response
Interestingly, the Stereoize Setting II has significantly less intensity when compared to Setting I; therefore, I recommend increasing the Depth for Setting II when a/b’ing; I found doubling it worked well.
Both Stage One and Ozone Imager sound smooth and transparent; however, Ozone Imager allows the user to change the density of the filter bands. Depending on the sound source, this can be particularly important; for instance, a hi-hat may sound artificial in the high frequencies with a larger delay setting, as the filter bands are very narrow and compact. Nevertheless, Stage One sounded excellent when tested on various sound sources.
PHASE RESPONSE
Stage One Mono Spread 25, Width -100 Phase Response
Stage One Mono Spread 100, Width -100 Phase Response
Stage One does not have a mono parameter; however, Width can be set to -100, which has the same effect. Stage One has excellent mono compatibility, particularly at low to moderate settings.
The Ozone Imager in Hybrid or Digital mode has a linear phase response when collapsed to mono at any setting and is, therefore, 100% mono-compatible.
Therefore, the Ozone Imager is recommended if mono compatibility is paramount, especially for more extreme settings. Otherwise, both plug-ins sound excellent on a wide range of sound sources.
M/S PROCESSING
The Width parameter in Stage One and the standard mode in Ozone Imager (not Stereoize) is basic M/S processing. The sound source must be stereo for this processor to work; if the source is mono, then Mono Spread or Stereoize must be enabled to create differences between the channels for additional widening.
Stage One Mono Spread 25, Width 0 Frequency Response
Stage One Mono Spread 25, Width 25 Frequency Response
The above images depict a mono signal stereoised by Mono Spread in the first image. Then, the magnitude of the inter-channel difference increased by Width in the second image, creating an even wider stereo field.
PHASE RECOVERY
Phase Recovery in Stage One and Recover Sides in Ozone Imager attempts to recover out-of-phase information in the side channels. There are some notable differences between these plug-ins:
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Ozone Imager has a single enable control for Recover Sides, whereas Stage One is band-independent. In practice, this is not an issue, as the Ozone Imager still allows for independent processing of each band via the sliders; however, if you did not want to Recover Sides in high frequencies while collapsing the signal to mono but allow it in the low band, or have different recovery amounts for each band (which is not available with Stage One) this cannot be achieved with a single instance of the plug-in.
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Stage One recovers phase information for both mono and stereo signals, whereas the Ozone Imager will only recover phase if the signal is moved towards mono.
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Ozone Imager allows for adjustment of how much information is recovered, whereas Stage One is an automatic process.
Frequency Dependent Phase Response
The above image illustrates a manufactured -0.6 out-of-phase signal at 100 Hz utilising a traditional Hass effect, approximately 150 degrees out-of-phase.
Stereo Image
And the stereo image of the same signal.
Stage One Phase Recover Enabled in the Low Band Frequency Dependent Phase Response
Stage One Phase Recovery was enabled in the low band and shifted the out-of-phase information into in-phase information, 0.2, about 80 degrees.
Stage One Phase Recover Enabled in the Low Band Stereo Image
Notice how the signal is wider in the low frequencies after Stage One has recovered the out-of-phase information, while the mid and high-frequency energy remains the same.
There is a misconception that out-of-phase information is “wider” than in-phase information, which is untrue. To explain, a phase correlation meter has +1 at the top, 0 in the middle, and -1 at the bottom: at +1, the signal is fully correlated (mono), and there are zero degrees of phase difference between the channels; at 0, the signal is fully decorrelated (stereo), there are 90 degrees of phase difference between the channels; and at -1, the signal is fully out-of-phase (polarity inverted dual mono), and there are 180 degrees of phase difference between the channels (which will cancel each other out when collapsed to mono) .
Ozone Imager Side Recover Enabled Frequency Dependent Phase Response
The above image shows the Ozone Imager with a setting of -30 and 18 dB in the Side Recovery to match the Phase Recovery of Stage One.
Ozone Imager Side Recover Enabled Stereo Image
The Ozone Imager has also widened the stereo image in the low frequencies; however, it is weighted towards the left-hand side in this example; I believe this is related to driving the Side Recovery to +18dB, 0dB or lower are often most optimal settings.
Phase Recovery in Stage One enables recovery of out-of-phase information for stereo signals; this feature should not be overlooked. For example, Haas-effected synths could be made wider with better mono compatibility with this feature. However, Ozone Imager allows for the recovery amount of side signal, which could be useful, particularly at low frequencies.
PREVENT ANTI-PHASE
Isotope Ozone Imager provides a setting labelled “Prevent Anti-Phase”, which limits inter-channel phase difference to 90 degrees.
To test this function, two phase-locked periodic waveforms were panned hard left and right with a combined output level of -6dB. With an M/S matrix and phase correlation meter on the output channel.
90 Degree Inter-Channel Phase Difference: Prevent Anti-Phase Enabled; Ozone +100
In the above test, Ozone Imager was configured in wideband mode with Prevent Anti-Phase enabled. As expected, at unity, there was no difference in level or inter-channel phase difference, similarly, increasing the slider had no effect, as the signal already had 90 degrees of inter-channel difference. The level also remained at unity 6dB combined, 12dB mid signal and 12dB side signal. This is also expected, as at 90 degree of inter-channel phase difference and at equal level, both the mid and side channels have equal power. Ignoring phase for a moment, it is a common misconception that a hard panned source like a synth or guitar have more signal in the side channel; however, both the mid and side have equal power.
60 degree Inter-Channel Phase Difference: Prevent Anti-Phase Enabled; Ozone 0
60 Degree Inter-Channel Phase Difference: Prevent Anti-Phase Enabled; Ozone 100
In the above examples, the inter-channel phase difference is modified to 60 degrees. When Ozone Imager is at unity the phase meter is at +0.5, and when the side signal is increased, phase difference is limited to 90 degrees (0), even when slider is at +100.
60 Degree Inter-Channel Phase Difference: Prevent Anti-Phase Disabled; Ozone 100
And the same signal with "Prevent Anti-Phase disabled.
Due to the 60 degree of inter-channel difference, while the combined output remains at -6dB in the unity version; as expected, there is a difference in the mid/side levels, with the mid channel at -9.5dB and the side channel at 15.5dB.
In the example that has “Prevent Anti-Phase” enabled and the slider at +100, the mid channel remaines at unity at -9.5dB, and the side channel increases to 11dB (a boost of 4.5dB). In the example where “Prevent Anti-Phase” is disabled, the mid channel remains at unity at 9.5dB, and the side signal is increased to 9.5dB (6dB boost), which is equal to the mid channel.
What can we conclude from the above tests? When inter-channel phase difference is 90 degrees or below, Ozone Imager is fully mono-compatible, with no difference in the mid channel at any setting of the slider (this is the same in Multiband mode if crossovers are set to Hybrid or Digital). When Prevent Anti-Phase" is enabled inter-channel phase difference is limited to 90 degrees, regardless of the settings. When “Prevent Anti-Phase” is disabled, dependent on inter-channel phase difference, side signal can be increased to be louder than the mid signal.
180 Degree Inter-Channel Phase Difference: Prevent Anti-Phase Enabled; Ozone 0
180 Degree Inter-Channel Phase Difference: Prevent Anti-Phase Enabled; Ozone 100
In the above examples, when Ozone Imager is at unity, the phase correlation meter is at -1 (180 degrees of phase difference), and the signal is at -6dB combined, with mid signal at DC, and side signal at -6dB. However, when the slider is modified, even by 1, the signal is attenuated by 6dB, if the signal had 90 degrees of inter-channel difference, this would mean that the mid and side signals had equal power. In this case, it simply attenuates the side signal by 6dB.
180 Degree Inter-Channel Phase Difference: Prevent Anti-Phase Disabled; Ozone 100
The same test with “Prevent Anti-Phase” disabled. When the slider is at +100, this signal is increased by 6dB, of course only in the side channel, as the mid channel is at DC.
What can we conclude from the above tests? At unity gain, there is no difference between “Prevent Anti-Phase” being enabled or disabled. I thought there was at first but further testing disproved this notion. When “Prevent Anti-Phase” is enabled, signal that exceeds 90 degrees of inter-channel phase difference will be immediately removed regardless of the setting of the slider in either direction. This is not good, as you are losing signal in these cases, I strongly recommend leaving this setting disabled for the majority of applications, especially mastering. However, it is worth emphasising this was a periodic waveform with 180 degrees of inter-channel phase difference, this is not a practical application by any stretch of the imagination, the side signal may be attenuated by a dB or so maximum in the real world.
An example where “Prevent Anti-Phase” may be useful is when widening mono or nearly mono sources and you do not want the side signal to exceed the level of the mid signal. While mono compatability (or better said, no audible effect to the mid signal) is guaranteed regardless of this setting, a louder side signal in relation to the mid rarely sounds good, often sounding disjointed and jarring to the listener.
DEPTH
Depth in Stage One adds early reflections to the signal. The parameter is a wet/dry control and is band-specific.
Impulse Response of a Click
Stage One Depth 25 Impulse Response
Stage One Depth 100 Impulse Response
Depth adds 400 milliseconds of early reflections to complete silence or 200 milliseconds to RT60, which is how reverb time is calculated when the decay has attenuated to -60 dB. As Danny said in Test Kitchen, this could be a great tool in mastering to add a subtle amount of Depth.
I noticed that Depth was effective for smoothing out signals that had considerable width processing; for example, Mono Spread and Width at +100 could sound a little disjointed, and adding a little bit of Depth filled in the gaps between the channels, creating a smooth and more natural sound.
CENTER GRAVITY
This is a balance/pan control for the mid-signal; for instance, if the phantom centre of a sound is off-centre, utilising a traditional pan pot would also shift the side signals, which would centre the mid-signal but change the side information. This control enables the mid signal to be panned separately from the side signal and is great for rebalancing program material.
PROCESSING MODE
Ozone Imager allows for separate processing of transient and sustained signals. This feature could be particularly effective for widening transient energy and narrowing sustained information for low-frequency content such as bass and 808s.
CONCLUSION
Both Stage One and Ozone Imager are excellent-sounding stereo widening plug-ins, and both will see regular use in my mixing and mastering work. The Ozone Imager offers more flexibility for widening signals, as it has four independent bands for processing compared to three in Stage One. It also includes a delay parameter that allows for fine-tuning the frequency band spread between channels. Ozone Imager has two Stereoize settings, although I often prefer I in the vast majority of cases. Phase Recovery in Stage One allows for phase recovery of stereo information without narrowing the stereo image and is also enabled/disabled per band. Recover Sides in Ozone Imager is enabled/disabled for all bands and requires narrowing of the stereo image to begin processing, so it is not as effective for recovering out-of-phase information in stereo signals. However, Ozone Image provides an amount parameter to fine-tune the dB amount of recovered sides to be represented in the mid signal. This control could be particularly useful for balancing the width of low-frequency energy. Depth is unique to Stage One in this comparison. It is very effective for adding a subtle sense of Depth to the signal, particularly effective for smoothing out heavily widened sources. Center Gravity in Stage One is a useful feature when you want to adjust the mid signal independent of the side signal. It is probably not a feature you will use often, but it is there for when it is needed. Transient/Sustain channel processing mode in Ozone Imager could be useful when separate processing of the transient and sustained energy is required.
I hope this post is as enjoyable to read as it was to write; I look forward to any discussion below.