Nebula (spatial spectrogram)
Principle of operation
Nebula / Spatial Spectrogram provides a unique representation of the audio material in terms of spectral content and localization in the stereo and/or surround space. Its combines the functionality of a spectrum analyzer and a vector scope in a novel real-time display. As such it provides to be an invaluable tool to get a complete and detailed overview of your mix, which you can finely tune in many aspects to suit your particular needs and preferences. A lot of work has gone into optimizing the real-time rendering of the display, not solely for aesthetic reasons, but because we wanted the display to react instantly to all the details in the incoming audio. The idea is literally for you to be able to see what you hear and feel, and not some gross simplification wrapped into shiny eye-candy, however pleasing to the eye.
The overall principles behind Nebula / Spatial Spectrogram are quite straightforward:
At any given time, and for every frequency, the engine computes the position of a frequency in space (2D in stereo , ND for N channel-surround). This position is taken as the center of gravity of the various channels, weighted by the relative amplitude of the signal in their corresponding channel.
A projection onto an LR-spectrum plane is computed, giving a spectrum-space frame constrained to the stereo field.
Incoming spectrum-space frames are added back to the previous frames.
Past frames are progressively “forgotten”, using blur and dimming, in order to make place for new information, and increase legibility.
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| Nebula / Spatial Spectrogram display with stereo input | Nebula / Spatial Spectrogram display with surround input |
Nebula / Spatial Spectrogram setup options
Scale
Focus
Controls the stereo image width X-axis display range, in dB.
A value comprised between ±18 and ±24dB correlates well with our abilities in perceiving the stereo image.
Default is ±18dB.
Pixels outside the focus range are clamped to the view boundaries.
AutoScale
This parameter controls whether the intensity of the particles are modulated by the overall audio level variations. In essence, when enabled, the color nuances will vary according to the relative amplitude of a frequency, allowing to monitor the relative amplitude spectrum variations. When disabled, the color will reflect the absolute audio level. You can also think of this as a kind of auto-gain setting.
AutoScale release
This controls whether color variations should be smoothed in time or not. When engaged, color variations is slowed down a bit, which makes overall level transitions more obvious.
You should to enable this setting when you want to visualize quick level variations such as those that frequently occur in movie soundtracks.
Linear blend range
Adds a constant blend amount to the particle. This ensures some particles are always blended into the image even if its original magnitude is low.
A low value for this setting has the effect of stabilizing the appearance of particles. With large values more of the spectrum dynamics are taken into account, and only peaks mostly come through.
Log blending
Toggles between linear and logarithmic blending of the current particle with old particles.
The default is off, i.e. linear blending, which tends to favor the display of peaks.
Logarithmic blending on the other hand preserves more of the full dynamic range of the data, and also gives some visibility to lower levels.
Display
Fading
Controls display persistence, i.e. the “fade to black” amount for a frame. Lowering this value retains past particles longer, whereas increasing this make them disappear faster.
Size factor
Controls the size of individual particles with respect to screen size.
Blur kernel size
Controls the radius of the blur effect applied to past particles. Particles are “smeared” more and more as they become older, depending on this setting. Naturally, a bigger value increases the smearing, at the expense of processing power.
Choosing the value for this setting is really matter of taste, although please keep in mind values that above 5 will require a sufficiently powerful graphics card in order to maintain a responsive display.
Particle scaling
Toggles automatic adjustment of particle size with screen size. When enabled, the overall aspect of the display will remain similar even if the view size changes.
Color mode
Provides the following particle-coloring modes: * Power: the color varies according to the power of the signal in the frequency region * Dynamics: same as previous except this mode works on signal dynamics * Power / dynamics: a mix of the above * Frequency: the color varies according to frequency only, using a rainbow-palette