SNR Calculator
SNR (dB)
60
How it works
Signal-to-Noise Ratio (SNR) measures the relative strength of a desired signal compared to background noise. SNR (dB) = 10 × log₁₀(P_signal / P_noise) = 20 × log₁₀(V_signal / V_noise).
**SNR thresholds** SNR = 0 dB: signal equals noise power (barely detectable). SNR = 10 dB: signal 10× noise power (marginal). SNR = 20 dB: signal 100× noise power (good quality). SNR = 40 dB: signal 10,000× noise power (excellent). Audio: SNR > 90 dB for high-fidelity recording (equivalent to 16-bit digital audio). Wi-Fi: SNR > 25 dB for reliable connection; SNR < 10 dB causes frequent disconnections.
**Noise sources** Thermal (Johnson-Nyquist) noise: fundamental limit, from random electron motion in resistors. P_noise = k × T × B, where k is Boltzmann's constant, T is absolute temperature, B is bandwidth. Shot noise: from discrete nature of electric charge. Flicker (1/f) noise: dominant at low frequencies in semiconductors. Quantization noise: in ADCs, from rounding analog values to discrete levels.
**Noise figure** Noise figure (NF) quantifies how much a device degrades SNR: NF (dB) = SNR_in (dB) - SNR_out (dB). An amplifier with NF = 3 dB halves the SNR. Low-noise amplifiers (LNA) at the front of a receiver chain are designed for minimum NF because noise added there is amplified by all following stages (Friis formula).
**ADC resolution and SNR** The theoretical maximum SNR of an ADC: SNR_max = 6.02 × N + 1.76 dB, where N is the number of bits. A 16-bit ADC has theoretical max SNR = 98 dB. ENOB (effective number of bits) accounts for real-world noise: ENOB = (SNR_actual - 1.76) / 6.02.
Frequently Asked Questions
- Wi-Fi SNR guidelines: <10 dB — connection unreliable/dropped. 10–25 dB — marginal, low throughput. 25–40 dB — good, supports most protocols. >40 dB — excellent, supports highest modulation schemes (1024-QAM, 4096-QAM in Wi-Fi 6E). Improve SNR by: moving closer to access point (signal strength increases), reducing interference sources (microwave ovens, baby monitors on 2.4 GHz), switching to 5 GHz or 6 GHz (less congested), using directional antennas, reducing obstructions (walls attenuate 3–15 dB each), or adding access points/mesh nodes. In 2.4 GHz: use only channels 1, 6, or 11 to avoid overlap with neighboring networks.
- SNR in audio = ratio of signal level to noise floor. Professional audio: SNR > 100 dB (24-bit digital = 144 dB theoretical dynamic range). Consumer audio: SNR 80–100 dB. Analog tape: 60–80 dB. Vinyl LP: 55–70 dB. Human hearing: ~120 dB dynamic range. Low SNR causes: audible hiss (random noise from preamp and ADC), limited dynamic range (quiet sounds buried in noise), and reduced bit-depth effectiveness (a 24-bit ADC with 80 dB SNR is effectively only 13.3 effective bits). To maximize SNR: use line-level inputs (not mic-level without a proper preamp), keep gain stages high early in the chain (gain before noise sources), and minimize cable length.
- Friis equation: P_received = P_transmitted × G_TX × G_RX × (λ / 4πd)². Taking 10log of both sides: P_RX (dBm) = P_TX (dBm) + G_TX (dBi) + G_RX (dBi) - FSPL (dB), where FSPL = 20log(4πd/λ). SNR = P_RX - Noise_floor. Noise floor = -174 dBm/Hz + 10log(bandwidth) + Noise_Figure. For a satellite link: TX power 20W = 43 dBm, dish gain 40 dBi, receive dish 35 dBi, FSPL 200 dB, bandwidth 1 MHz, NF 2 dB: P_RX = 43+40+35-200 = -82 dBm. Noise floor = -174+60+2 = -112 dBm. SNR = 30 dB.
- Johnson noise power scales with bandwidth: P_noise = kTB. Reducing measurement bandwidth reduces noise. A multimeter measuring DC uses a narrow effective bandwidth (averaging filter) — achieving high SNR for stable signals. An oscilloscope measuring fast signals needs wide bandwidth — noise is higher. The noise spectral density of a resistor at room temperature: e_n = √(4kTR) = 4 nV/√Hz for 1 kΩ. A 100 kHz bandwidth adds √100,000 × 4 nV = 1.26 µV RMS noise — significant for microvolt-level measurements. Lock-in amplifiers achieve sub-nanovolt sensitivity by using an extremely narrow noise bandwidth around the signal frequency.