[2.7] Equivalent Noise Level
47.What is the equivalent noise level?
Equivalent noise level indicates the self noise of a microphone produced by itself, this is commonly seen in condenser microphones. It’s measured in dB-A. The “A” stands for A-weighting, which refers to the loudness of air vibration relative to human perception.
48.What numerical value of equivalent noise level is best?
No one can tolerate a microphone with much noise, especially in professional usage like studio recording, while noise can not be controlled as low as zero. So what makes a good equivalent noise level?
- ≤ 15 dBA: It’s the best noise level range with indiscernible noises, usually realized in large-diaphragm microphones. And below 10 dB-A is extremely low self noise, but ambient noise is usually higher than 10 dB-A.
- 16-19 dB-A: It’s still good for most applications. Noise may be heard in a very quiet environment, but it’s not a noticeable issue.
- ≥20 dB-A: It’s obviously audible high self-noise level. It only may be workable for loud sound sources and microphones be placed closer to sound sources, so as to achieve a good enough signal-to-noise ratio. Microphones with over 25 dB-A are almost useless.
[2.8] Signal to Noise Ratio (SNR)
49. What is the signal to noise ratio?
In audio communications, the signal-to-noise ratio (abbreviated as S/N, or SNR) indicates the level of the audio signal relative to unwanted noise, measured by decibels (dB).
As explained in sensitivity, “pickup” level of the microphone is at 94 dB SPL per Pascal (Pa).
So make it more understandably, SNR = Sound pressure level (94 dB) − equivalent noise level
50.What numerical value of SNR is best?
- An ideal SNR means the maximum amount of signal and the least unwanted noise.
- As introduced previously, the best noise is below 15 dB, So the optimal SNR is 79 dB (94-15) and above.
- Generally, A microphone with SNR of over 75dB (94-19) is still a good level, and below 70dB is not so professional.
[2.9] Total Harmonic Distortion
51.What is total harmonic distortion?
Total harmonic distortion (THD) measures the distortion in an audio signal due to harmonics.
It is the ratio between the total values of all the harmonic frequencies to the fundamental frequency, expressed as a percentage.
52. What numerical value of THD is best?
The lower the THD figure, the less the distortion in microphone output and the more accurate audio reproduction.
When measuring a microphone’s maximum sound pressure level, the typical threshold is 1% THD.
A total harmonic distortion (THD) of below 0.5%, is hardly audible.
Here is a typical specification of a professional condenser microphone for recording, take SWOPOR UMK009 for example:
Sampling rate: 192KHz/24bit
Microphone core: Dia. 14mm / condenser
Polar pattern: Cardioid
Frequency response: 80Hz-20000Hz
Sensitivity: – 42 ± 3dB (1.5V, 680KΩ; 0dB = 1V / Pa, 1KHz)
Distortion degree: <-90dB(<0.003%)
Signal to noise ratio: >103dB