Signal-to-Noise Ratio (SNR)
Definition
Signal-to-Noise Ratio (SNR)
Signal-to-Noise Ratio (SNR) is the difference in decibels between the desired signal level and the noise floor of a system or environment. Higher SNR indicates cleaner audio reproduction with less audible noise. SNR is fundamental to measurement quality — SonaVyx requires adequate SNR for reliable transfer function, RT60, and STI results.
SNR = 20 × log₁₀(Vsignal / Vnoise) dB
How It Is Measured
SNR is measured by comparing the RMS level of the desired signal to the RMS level of the residual noise when the signal is absent. SonaVyx computes SNR automatically during measurements by analyzing the noise floor before the stimulus begins. For impulse response measurements, the Impulse-to-Noise Ratio (INR) serves as the SNR metric, with ISO 3382-1 requiring at least 35 dB INR for T20 and 45 dB for T30.
Practical Example
A microphone positioned 10 meters from a PA speaker in a noisy venue measures the pink noise stimulus at 82 dBA with a background noise floor of 65 dBA, yielding an SNR of 17 dB. This is borderline for transfer function measurement — SonaVyx coherence drops below 0.7 at low frequencies where background noise is strongest. Moving the microphone closer to 5 meters improves SNR to 23 dB and coherence rises above 0.85.
SNR Requirements for Acoustic Measurements
Different measurements require different minimum SNR levels. Transfer function measurement needs at least 10 dB SNR for meaningful coherence. RT60 measurement per ISO 3382-1 needs 35 dB INR for T20 and 45 dB for T30. STI measurement requires the test signal to be at least 15 dB above the background noise. SonaVyx warns users when SNR is insufficient for reliable results.
Improving SNR
The primary methods to improve measurement SNR are: increase the test signal level (louder stimulus), decrease the background noise (turn off HVAC, close doors), reduce the measurement distance (move microphone closer to the speaker), use averaging to reduce random noise (each doubling of averages adds 3 dB SNR), and use swept sine instead of noise stimulus (sweeps concentrate energy at one frequency at a time, achieving higher instantaneous SNR).
Dynamic Range vs SNR
SNR describes the ratio at a specific signal level, while dynamic range describes the total usable range from noise floor to maximum undistorted level. A system with a -94 dBu noise floor and +24 dBu maximum output has 118 dB dynamic range. If the operating level is +4 dBu, the SNR is 98 dB. Both metrics matter but describe different aspects of system performance.
Try It Now
Assess signal-to-noise ratio — free measurement in your browser