Question 1

What is the difference between RTA and FFT spectrum analysis?

Accepted Answer

An RTA (Real-Time Analyzer) displays the spectrum in octave or fractional-octave bands (1/1, 1/3, 1/6, 1/12), grouping FFT bins into perceptually meaningful bands. Each band width is proportional to its center frequency, matching human frequency resolution. An FFT analyzer displays the raw spectrum with constant-width frequency bins (e.g., 11.7 Hz per bin at 4096/48kHz). RTA is better for: tonal balance assessment, EQ decisions, noise criteria (NC/NR) comparison, and quick visual evaluation. FFT is better for: identifying discrete tones (hum, feedback), measuring room modes, analyzing narrowband phenomena, and scientific analysis. SonaVyx provides both modes: RTA with octave bars overlaid on the spectrum, and raw FFT with adjustable resolution. You can switch between them in real time.

Question 2

Why does pink noise look flat on an RTA but sloping on an FFT?

Accepted Answer

Pink noise has equal energy per octave (or any constant percentage bandwidth). On an RTA display, each bar represents one octave or fraction of an octave, so each bar captures the same energy — resulting in a flat display. On an FFT display, each bin has constant width in Hz. Higher octaves contain more bins than lower octaves (the 1-2 kHz octave has 86 bins at 11.7 Hz resolution, while the 125-250 Hz octave has only 11 bins). Since the same energy per octave is spread across more bins at higher frequencies, each bin gets less energy, causing the characteristic -3 dB per octave downward slope. This is a display artifact, not a measurement error. White noise (equal energy per Hz) appears flat on FFT but rises +3 dB/octave on RTA.

Question 3

Which is better for live sound system tuning — RTA or FFT?

Accepted Answer

Both are used, often together. RTA is better for quick tonal balance assessment: you can glance at the octave bars and immediately see if the system is too bright, too bass-heavy, or well balanced. It is also the standard display for matching to NC curves and making broad EQ decisions. FFT (with transfer function) is better for precise system alignment: identifying comb filtering, measuring phase relationships, finding feedback frequencies, and seeing the fine detail of room modes. Professional sound engineers typically start with RTA to assess the overall tonal shape, then switch to transfer function mode for detailed alignment and problem solving. SonaVyx unified workspace provides both in a single interface, switchable with keyboard shortcuts.

Question 4

Does RTA have better or worse frequency resolution than FFT?

Accepted Answer

RTA has proportional (percentage) resolution: a 1/3 octave band at 1 kHz is 232 Hz wide, but at 100 Hz it is only 23 Hz wide. FFT has constant (absolute) resolution: every bin is the same width (e.g., 5.9 Hz at 8192/48kHz). At low frequencies, FFT typically has better absolute resolution. At high frequencies, RTA bands are wider than FFT bins. However, comparing them directly is misleading because they serve different purposes. RTA resolution matches human frequency discrimination (we hear logarithmically), so it shows what humans perceive. FFT shows the physical reality. For resolving two tones 10 Hz apart at 100 Hz, you need FFT. For assessing whether a room sounds bright, RTA is more intuitive. SonaVyx applies fractional-octave smoothing to the FFT to achieve RTA-equivalent display.

Question 5

Can I convert between RTA and FFT views of the same data?

Accepted Answer

Yes. An RTA display is derived from FFT data by summing the power in all FFT bins within each octave band. This is exactly what SonaVyx does: it computes the FFT at full resolution and then groups bins into octave bands for the RTA overlay. Going the other direction (from RTA to FFT) is not possible because the octave-band grouping discards the fine frequency detail. This means you lose nothing by starting with FFT and deriving RTA, but you lose information going from RTA to FFT. In SonaVyx, both views are always available simultaneously — the RTA bars are overlaid on the FFT trace. You can toggle the bar overlay on or off without recapturing data.

Question 6

What is constant-Q analysis and how does it compare to RTA and FFT?

Accepted Answer

Constant-Q (CQ) analysis uses a bank of bandpass filters, each with the same Q factor (ratio of center frequency to bandwidth). This gives proportional bandwidth like RTA but with a smoothly varying frequency axis like FFT. The result is similar to 1/N octave RTA but without the discrete band edges. CQ analysis is computationally more expensive than FFT and is used in some musical analysis applications. For audio measurement, the practical difference between CQ and well-smoothed FFT is minimal. SonaVyx achieves the visual equivalent of constant-Q display by applying fractional-octave smoothing to the FFT output, which is computationally efficient and allows real-time adjustment of the smoothing bandwidth.

Question 7

Is RTA still useful when I have transfer function measurement available?

Accepted Answer

Yes. RTA serves different purposes than transfer function measurement. RTA shows what is actually happening at the microphone position, including the contribution of the program material. This is valuable for: monitoring overall SPL and frequency balance during a show, checking that the system is not too loud in any frequency range, verifying that the tonal balance sounds right to the audience, and assessing background noise without a reference signal. Transfer function removes the program content and shows only the system response, which is needed for EQ and alignment. During a live show, you might use transfer function (with a console feed reference) for system optimization and RTA on a separate mic for audience experience monitoring. SonaVyx supports running both simultaneously.

Question 8

How do I interpret an RTA display during a sound check?

Accepted Answer

During sound check, the RTA shows the combined effect of the source (instruments, vocals), the sound system, and the room. With pink noise as the source, the RTA directly shows the system+room response. With music or speech, the display fluctuates with the program content. Look for: overall tonal balance (should be roughly flat or match your target house curve), excessive bass buildup (common in smaller venues with parallel walls), a bright or harsh midrange (2-4 kHz peak, common with horn-loaded speakers), insufficient high-frequency content (may indicate angled speakers or damaged tweeters), and the consistency of the display between different program material. If the response looks similar regardless of what is being played, the features you see are system characteristics. SonaVyx peak hold mode captures the maximum levels at each frequency over the sound check for analysis.

RTA vs FFT Analyzer: When to Use Each for Audio Measurement

Frequently Asked Questions