Spectrum and Spectrogram

Spectrum and Spectrogram

Spectrum and Spectrogram both show frequency content, but answer different questions. Spectrum is an immediate slice of the signal; Spectrogram preserves a scrolling history.

Spectrum

Use Spectrum to inspect tonal balance, dominant notes, resonances, and changing energy across the frequency range.

Spectrum controls

Control	Choices	What it changes
FFT Size	1024, 2048, 4096, 8192, 16384	Frequency separation versus response speed and processing cost. Default: 2048.
Scale	Log, Mel, Linear	How frequencies are spaced across the display. Default: Log.
Range	Extended, Audible	Extended requests 10 Hz–24 kHz; Audible requests 20 Hz–20 kHz. Both stop at the capture Nyquist frequency.
Peak	Off, On, Following	Shows the strongest stable frequency in a fixed or moving overlay. Default: Off.
Smoothing	0–0.99	How strongly successive curves are averaged. Default: 0.90.
Tilt	0–6 dB/oct	Visually compensates for the usual high-frequency falloff. Default: 2 dB/oct.
Fill	On/Off	Fills the area beneath the live curve. Default: On.
Grid	On/Off	Shows frequency and level guides. Default: On.
Side	On/Off	Adds separate side-channel frequency information. Default: Off.

Scale, range, tilt, and smoothing change the analysis presentation only. They do not apply EQ or alter playback.

Peak readout

Peak finds the strongest stable frequency and reports its level, frequency, and nearest musical note.

• Off hides the readout.
• On keeps the result in a fixed overlay.
• Following places the overlay near the detected peak while keeping it inside the scope.

Peak detection is most useful for sustained tones. Percussion, noise, and dense mixes can make the result move rapidly or favor a strong harmonic instead of the fundamental.

Heatmap

Enable Heatmap to retain recent frequency energy behind the live curve. It is useful for seeing short events and distinguishing persistent content from a momentary peak.

• Heat Tilt adjusts the heat layer independently from the live Spectrum curve from 0–6 dB/oct. Default: 2.
• Heat Smoothing controls how steadily the heat layer changes from 0–0.99. Default: 0.50.

The heatmap is off by default. Raising smoothing makes broad patterns easier to see but can conceal fast changes.

Spectrogram

Use Spectrogram when the timing of frequency events matters. Each new slice is added to a scrolling history, so attacks, decays, sweeps, noise, harmonics, and repeating patterns remain visible.

Spectrogram controls

Control	Choices	What it changes
FFT Size	512, 1024, 2048, 4096, 8192	Frequency detail versus time detail and processing cost. Default: 4096.
Scale	Log, Mel, Linear	Frequency spacing. Default: Log.
Range	Extended, Audible	Requested display range, limited by the source sample rate. Default: Extended.
Clarity	Classic, Focused, Sharp, Sharper	How time/frequency energy is resolved. Default: Sharper.
Color	Heat, Solid	Heat uses intensity color; Solid uses the theme foreground. Default: Heat.
Speed	1–8	Scroll rate and the amount of history visible. Default: 2.
Contrast	0.5–2.0	Separation between faint and strong content. Default: 1.0.
Tilt	-2–8 dB/oct	Frequency-dependent display compensation. Default: 4 dB/oct.
Frequency Grid	On/Off	Shows frequency guides over the history. Default: On.

Classic gives a conventional FFT history. Focused uses Prism's earlier focused presentation. Sharp and Sharper preserve more detail with frequency reassignment; they can make tonal lines and transient structure more distinct at additional processing cost.

Scale and range tips

• Start with Log for music because octaves receive similar visual space.
• Try Mel when perceptual spacing is more helpful than exact octave spacing.
• Use Linear for technical inspection where equal hertz intervals should have equal width.
• Choose Audible when you want consistent 20 Hz–20 kHz labels.
• Choose Extended to include sub-20 Hz content and any captured content above 20 kHz.

At a 44.1 kHz capture rate, the upper limit is about 22.05 kHz even when Extended requests 24 kHz.

Rotation, mirroring, and measurement

Both scopes support 0°, 90°, 180°, and 270° rotation plus horizontal mirroring. These controls transform the complete canvas and are useful for narrow vertical overlays.

Press and drag within either scope to show its measurement crosshair. Spectrum reports the frequency and level under the pointer. Spectrogram reports the time/frequency position and intensity represented by that point. The overlay remains aligned after rotation or mirroring.

Practical starting points

• For a responsive general-purpose Spectrum, keep 2048, Log, Extended, and moderate smoothing.
• For closely spaced bass notes, raise Spectrum FFT size and accept slower movement.
• For short attacks in Spectrogram, try a smaller FFT or a faster history speed.
• For sustained harmonics, use a larger FFT with Sharp or Sharper clarity.
• If the display is visually crowded, turn off Fill, Heatmap, or Frequency Grid before changing the underlying analysis.

See Understanding the Scopes for the common controls and analysis tradeoffs.