AES-2id Excitation Signals: Swept Sine and Alternatives
TL;DR
AES-2id recommends logarithmic (exponential) swept sine as the primary excitation signal. Key specifications: frequency range should cover at least 20 Hz to 20 kHz, sweep duration 3-30 seconds (longer = higher SNR), sample rate ≥44.1 kHz (48 kHz preferred), fade-in/out of 10-50 ms to avoid transients, pre-silence ≥0.5 s, post-silence ≥ expected RT60. The sweep rate is constant octaves per second: f(t) = f1·exp(t·ln(f2/f1)/T). Logarithmic sweep provides time-separated harmonic distortion products during deconvolution, unlike linear sweep or MLS.
Logarithmic Swept Sine
The logarithmic (exponential) sweep is generated by:
x(t) = sin[ 2π·f₁·T/ln(f₂/f₁) · (exp(t·ln(f₂/f₁)/T) - 1) ]
Where f₁ is the start frequency, f₂ the end frequency, and T the sweep duration. The instantaneous frequency increases exponentially, spending equal time per octave. This matches the logarithmic frequency resolution of human hearing and acoustic analysis.
Duration Selection
Sweep duration affects measurement SNR directly:
| Duration | SNR improvement vs 1s | Typical use case |
|---|---|---|
| 3 seconds | +5 dB | Quick survey, quiet rooms |
| 10 seconds | +10 dB | General-purpose measurement |
| 20 seconds | +13 dB | Large venues, high precision |
| 30 seconds | +15 dB | Maximum quality, research |
Doubling the sweep duration adds approximately 3 dB of SNR. For meeting ISO 3382-1 INR requirements, 10-20 second sweeps are typically sufficient with a decent loudspeaker.
Bandwidth and Sample Rate
The sweep should span at least 20 Hz to 20 kHz for full audio-band characterization. AES-2id recommends starting slightly below 20 Hz (e.g., 10 Hz) and ending above 20 kHz (e.g., 22 kHz) to ensure the useful band has full energy. Sample rate should be 48 kHz for professional audio work (matching common PA system rates).
Fade-In/Fade-Out
Abrupt signal onset creates broadband transients that contaminate the impulse response. AES-2id recommends cosine-squared fade-in of 10-50 ms at the sweep start and fade-out at the sweep end. The fade duration should be short relative to the sweep duration but long enough to suppress spectral leakage.
Pre/Post Silence
Include at least 0.5 seconds of silence before the sweep to capture the noise floor for SNR assessment. Post-sweep silence must exceed the expected reverberation time — if the room has RT60 = 3 s, include at least 4 s of post-silence to capture the full decay. Truncating the reverberant tail corrupts the deconvolution.
MLS Alternative
Maximum Length Sequences offer constant sound level (no crest factor issues) and are computed via circular cross-correlation. However, MLS is more sensitive to time variance and does not separate harmonic distortion. AES-2id recommends swept sine over MLS for most applications.
SonaVyx Implementation
The impulse response tool generates logarithmic sweeps with configurable duration (2-20 s), automatic fade-in/out, and appropriate pre/post silence. MLS generation (orders 2-18) is also available. See signal processing for the deconvolution step and common errors to avoid.
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Last updated: March 19, 2026