Question 1

What is an impulse response and what information does it contain?

Accepted Answer

An impulse response (IR) is the time-domain output of a system when excited by a perfect impulse (infinitely short, infinitely loud click). In practice, we obtain it by deconvolving a measured output from a known input signal. The IR contains all the information about the system: the direct sound arrival (propagation delay), early reflections from nearby surfaces (first 50-80 ms), late reverberation (diffuse decay), frequency response (via FFT of the IR), phase response, and room acoustic parameters (RT60, C50, C80, D50, Ts). A single IR measurement is mathematically equivalent to measuring the transfer function at all frequencies simultaneously. SonaVyx captures impulse responses using logarithmic sine sweeps and MLS signals, then derives all acoustic parameters from the IR.

Question 2

How does sweep deconvolution work to extract an impulse response?

Accepted Answer

A logarithmic sine sweep excites each frequency sequentially from low to high. The recorded response contains the sweep convolved with the room impulse response. Deconvolution reverses the convolution by dividing in the frequency domain: IR(f) = Output(f) / Sweep(f). In practice, SonaVyx uses an inverse filter designed to match the sweep spectrum, so multiplication replaces division (avoiding divide-by-zero issues). The inverse filter also time-reverses and amplitude-compensates the sweep, concentrating the spread-out energy back into a compact impulse. A key advantage of log sweeps is that harmonic distortion products appear at negative times (before the main impulse), so they can be cleanly separated from the linear IR by windowing. This makes sweep deconvolution robust even with nonlinear systems.

Question 3

What is MLS and how does it differ from a sweep for IR capture?

Accepted Answer

MLS (Maximum Length Sequence) is a deterministic pseudo-random binary signal with a flat power spectrum. The IR is extracted via circular cross-correlation between the recorded output and the original MLS signal. Key differences from sweeps: MLS excites all frequencies simultaneously (faster measurement), but it is sensitive to time-varying conditions (if anything changes during measurement, artifacts appear as raised noise floor). MLS cannot separate harmonic distortion from the linear response. MLS requires the system to be time-invariant during the entire measurement. Sweeps are more robust in practice because they tolerate moderate time variance and isolate distortion. SonaVyx supports both methods: use sweeps for general room acoustics and use MLS for controlled environments where speed matters, such as automated production-line testing.

Question 4

What equipment do I need to capture a room impulse response?

Accepted Answer

Minimum setup: a computer or phone running SonaVyx, a speaker to generate the test signal, and a microphone to capture the response. For quality results: use a measurement microphone with flat frequency response (miniDSP UMIK-1, Behringer ECM8000, or similar). The speaker should be capable of reproducing the full frequency range of interest. For ISO 3382 compliance, use an omnidirectional speaker (dodecahedron) that radiates equally in all directions. For system measurement, use the installed sound system as the source. Place the microphone on a stand at ear height (1.2 m seated, 1.5 m standing), away from reflecting surfaces. SonaVyx generates the sweep signal through your speaker and captures the response through the microphone, performing the deconvolution automatically.

Question 5

How do I ensure a good signal-to-noise ratio for IR capture?

Accepted Answer

Signal-to-noise ratio (SNR) determines the usable dynamic range of the impulse response. Target at least 45 dB for reliable T30 analysis. Strategies: use the loudest source level practical without causing distortion or discomfort. Use a longer sweep (10-20 seconds concentrates more energy into the deconvolved impulse). Reduce background noise by measuring during quiet periods, closing doors and windows, and turning off HVAC if possible. Keep the measurement microphone away from noise sources. If SNR is still insufficient, average multiple measurements (each +3 dB per doubling). SonaVyx displays the INR (impulse-to-noise ratio) after each measurement so you immediately know if the quality is sufficient. The measurement wizard warns if INR is below the threshold for your selected analysis parameters.

Question 6

Can I capture an impulse response using a single device (phone or laptop)?

Accepted Answer

Yes, SonaVyx supports single-device loopback mode where the same device generates the test signal through its speaker and captures the response through its microphone. The main challenge is acoustic echo cancellation (AEC) in the browser, which tries to remove the played signal from the microphone input. SonaVyx uses an AEC bypass cascade: first attempting a sweep through an HTML audio element, then falling back to WebRTC loopback, MLS, or click train if the signal is not detected. For best results with a single device, use an external speaker positioned away from the microphone, use headphones to prevent feedback, or use a separate USB microphone. Multi-device mode (one device plays, another records) avoids AEC issues entirely.

Question 7

What sweep length should I use for impulse response capture?

Accepted Answer

Sweep length affects signal-to-noise ratio, low-frequency resolution, and measurement time. Guidelines: for small rooms (RT60 under 1 second), a 2-5 second sweep is sufficient. For medium rooms (RT60 1-2 seconds), use 5-10 seconds. For large reverberant spaces (churches, concert halls, RT60 above 2 seconds), use 10-20 seconds. The sweep should be at least 2-3 times the expected RT60 to ensure the complete decay is captured. Longer sweeps also improve low-frequency SNR because more cycles of low frequencies are included. The total measurement time is sweep length plus the expected RT60 (to capture the full decay). SonaVyx defaults to 5 seconds and recommends longer durations based on room size input in the measurement wizard.

Question 8

How do I avoid capturing unwanted noise in my impulse response?

Accepted Answer

Sources of noise contamination include: HVAC systems (turn off if possible or measure during quiet periods), traffic (measure late at night or early morning), electrical interference (keep microphone cables away from power cables, use balanced connections), mechanical vibration (use a shock-mounted microphone stand, avoid placing on a vibrating surface), and human activity (clear the room of people and ensure doors are closed). Wind from HVAC vents directly hitting the microphone is a common problem — use a foam windscreen or reposition the mic. After capture, check the impulse response tail: it should decay smoothly into the noise floor without bumps or spikes from transient noise events. SonaVyx INR display and visual IR waveform help you identify contamination immediately.

Impulse Response Capture: Sweep Methods, MLS, Equipment, and Best Practices

Frequently Asked Questions