Audio quality is measured by Signal-to-Noise Ratio, Frequency Response, and Total Harmonic Distortion, plus perceptual tests like PEAQ.
How to Measure Audio Quality? The process involves three core electrical specifications: Signal-to-Noise Ratio (SNR), Frequency Response, and Total Harmonic Distortion (THD). Engineers also use standardized perceptual methods like the ITU‑R BS.1387‑2 PEAQ to evaluate how audio sounds to the human ear. No single number tells the whole story — a full measurement suite is required.
What Are the Key Audio Quality Metrics?
Each metric targets a different type of signal degradation. Below are the five most important ones every engineer should know.
| Metric | Definition | Good Value |
|---|---|---|
| Signal-to-Noise Ratio (SNR) | Ratio of signal power to background noise power (excluding harmonics), measured in dB. | 90 dB or higher |
| Frequency Response | Flatness of output over the 20 Hz–20 kHz audible band; 1 kHz is set as 0 dB reference. | ±3 dB across 20 Hz–20 kHz |
| Total Harmonic Distortion (THD) | Ratio of harmonic content to the original test signal (using a notch filter to remove the fundamental). | Well below 1% (e.g., 0.05%) |
| Dynamic Range | Ratio of the full‑scale signal to the rms noise floor, measured with a small signal (−40 or −60 dBV). | 100 dB or more for digital devices |
| PEAQ (Perceptual Evaluation of Audio Quality) | Objective measurement using psychoacoustic models; the only standardized method per ITU‑R BS.1387‑2‑202305. | Output as a subjective difference grade (SDG) |
These metrics together paint a complete picture. For example, a device might have excellent SNR but poor frequency response, or low THD but a limited dynamic range. That’s why audio system measurements always include a battery of tests rather than a single score.
How to Perform Standard Audio Measurements
Follow the engineering standard to get repeatable results. First, set the measurement bandwidth to 20 Hz–20 kHz, the test‑signal frequency to 1 kHz, the sample rate to 44.1 kHz, and ensure all attenuators are at zero. Then run the sequence:
- Measure SNR: Apply a −60‑dBFS signal with A‑weighting (20 Hz–20 kHz) to compensate for the ear’s frequency sensitivity.
- Measure Frequency Response: Sweep from 20 Hz to 20 kHz, with 1 kHz at 0 dB, and check spot frequencies at octave intervals.
- Measure THD/THD+N: Use a sinusoidal test signal with a notch filter to remove the fundamental, then calculate the ratio of residual harmonics and noise to the input.
Remember that measuring at the device output alone ignores the room. For true in‑ear or at‑the‑listening‑position quality, use a calibrated microphone and software like REW (Room EQ Wizard).
Once you understand these specs, you’ll know what to look for in gear. For tested product recommendations, browse our roundup of best audio quality earphones that deliver on these measurements.
Common Measurement Tools and Methods
Hardware analyzers such as Audio Precision provide lab‑grade electrical measurements. For room and speaker testing, a Brüel & Kjær 4231 calibrator ensures microphone sensitivity remains stable. On the software side, tools like ViSQOL and POLQA perform intrusive analysis, while P.563 handles non‑intrusive evaluation. Regardless of the tool, always calibrate microphones beforehand to avoid data drift.
One frequent mistake: relying solely on one metric. SNR alone doesn’t capture frequency imbalance or harmonic distortion. Another common pitfall is testing only at the device output — the listening position is where real quality matters. Finally, keep impedance tests at small signal levels so the driver stays within its linear pistonic range.
FAQs
What is a good SNR for audio?
A Signal-to-Noise Ratio of 90 dB or higher is considered excellent for most listening scenarios. Consumer gear often falls between 80–100 dB, while professional equipment can exceed 120 dB.
Can you measure audio quality with software alone?
Software can perform perceptual analysis (e.g., PEAQ) and calculate metrics from recorded files, but accurate electrical measurements like THD require a hardware analyzer and a calibrated test signal.
What is the difference between THD and THD+N?
THD measures only the harmonic distortion products, while THD+N includes both harmonics and the noise floor. THD+N is more common because it reflects real‑world conditions, but a true THD value isolates distortion from background noise.
References & Sources
- Audio System Measurements. “Audio system measurements” Comprehensive overview of standard metrics and procedures.