VIDEO SERIES
Audio measurements and results
This training series outlines key measurements for audio products, specifically signal-to-noise ratio, crosstalk and gain, intermodulation distortion, frequency response and phase, THD+N and level. These videos explain the basic principles of each measurement, why they are significant and how to test and calculate correctly.
Audio Amplifier Characteristics Explained: Part 1
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Welcome to TI's basics to audio measurements and results part 1, discussing SNR, crosstalk and gain. The first will be signal-to-noise ratio. Signal-to-Noise Ratio, or SNR, is a measurement that describes how much noise is in the output of a device in relation to the signal level.
Every device has a certain amount of noise at its output. A small amount of noise may not be objectionable if the output signal is very strong. In many cases, the noise may not be audible at all.
With a large amount of noise, it may overpower the output signal and become the dominant output from the device. To make the determination objectively, we need to look at the relative strength of the output signal and the noise level-- or to put it in another way, the signal-to-noise ratio.
The SNR is calculated with the desired output from the device divided by the background noise. This can be expressed as either a percentage or as a decibel value. The DB value is calculated by using 20 log desired signal divided by noise.
The ratio can produce small and large numbers. The units are often expressed in decibels, as it is easier to express a large range of numbers in this logarithmic scale. Here we have different sounds on the exposure time for the DB level, as well as the relative loudness of different decibel increases.
Now, for crosstalk. Crosstalk is when a signal transmitted on one channel creates an unwanted effect on another channel. This can be easily measured. If a signal is simulated through channel 1 and then the output is measured through channel 2, if any signal is measured at the output, then it is crosstalk from channel 1.
The value for this output signal is then divided by the input signal into channel 1. And the ratio is the value of the crosstalk. This can be expressed in decibels. When there is multiple signals, it can get difficult to analyze all of the combinations of channels off and on. So you can use a multichannel audio analyzer.
Gain is the increase or decrease in the amplitude level of an audio signal. This is usually defined as the output signal amplitude or power divided by the input signal amplitude or power. The ratio between the two will determine the gain of a signal.
This can also be expressed in DB. Expressed in DB, it is 20 log Vout over Vin. This means that with an output signal that is two times the size of the input signal, the gain of the signal is 2. But expressed in decibels, it is 6.02 DB.
