- Signal-to-Noise Ratio

SIGNAL-TO-NOISE RATIO (SNR) – REAL LIFE EXAMPLES

You cannot eliminate noise from electronic recording equipment, such as digital audio recorders, camcorders, DSLR video cameras, etc.  The name of the game is to optimize the signal-to-noise ratio (SNR).  But, what is signal-to-noise ratio? 

EXAMPLE OF SNR PRINCIPLE

For a real world example, listen to this audio clip.  As humans, we adjust our environment to achieve a minimum signal-to-noise ratio that is pleasing to the human ear.  In the audio clip, as the noise increases, we need to turn up the radio (signal) until we get to the point where we’ve reached that pleasing minimum signal-to-noise ratio.

EXAMPLE OF SNR "LONG POLE IN THE TENT"

In the above example, the SNR could be improved because we can turn up the signal level (radio) independent of the noise level (road noise).  But, if the two linked together, then turning up the signal level would not improve the signal to noise performance.  For a real world example of this, listen to the second audio clip.  Because their radio receiver is already receiving a static-y signal, turning up the volume control turns up both the signal AND noise TOGETHER, resulting in no improvement in signal to noise performance.  The radio station signal has been attenuated so far so and its signal level is so low by the time it reaches our radio receiver antenna, that the radio signal level compared to the radio noise (sunspots, thermal, etc) is very poor when it hits our radio receiver antenna.  The SNR at that point is the "long pole in the tent" for the SNR in the system.  It can't get any better than that, no matter how kick-ass of a radio receiver we purchase.

This is analogous to a situation where your microphone is poorly placed (too far from the subject, resulting in the input signal been too low) or you are using a microphone with poor signal to noise performance specs.  Then, no matter how clean of a low noise preamplifier you use or how much you turn up it’s volume, there will be no improvement in signal to noise performance because the limit in the signal to noise performance has been set at the microphone (which has become the "long pole in the SNR tent").  A low-noise preamplifier can only improve the signal to noise performance of downstream components (camera, recorder), and can not improve the poor signal to noise performance of upstream components (microphone).  That is to say, garbage in … garbage out.