# AP - The Recognized Standard In Audio Test

## Introduction to the Basic Six Audio Tests

While there can be hundreds of audio measurements that are appropriate for any particular device, there are some basic audio measurements that are relevant to nearly all audio devices.

This series of videos looks at those Big Six audio tests -- Level & Gain, THD+N, Frequency Response, Crosstalk, Phase, and Signal-to-Noise Ratio.

We’ll discuss what each test measures and then how to make the measurement with an APx audio analyzer.

##### Level & Gain

Level, also known as amplitude, describes how big the signal is. The greater the amplitude of the signal, the higher the level. Level is probably the most basic audio measurement we can make: How much energy does our device output? What level can it output before it distorts the signal?

##### THD+N

THD+N stands for Total Harmonic Distortion plus Noise.

Harmonic distortion and noise come from different sources. An ideal sine wave has only one frequency. In the real world, though, imperfections (or "nonlinearities") in real devices modify or "distort" the wave, most often by adding harmonics.

##### Frequency Response

Frequency response measures the output level of a device at different frequencies.

Results are displayed on a graph showing level vs. frequency. Usually we’re looking to see if the response is flat.

##### 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 some amount of noise at its output. The question is, “How much is too much?” The answer is, “it’s all relative”.

##### Crosstalk

Crosstalk is unwanted leakage or bleed of a signal from one or more channels to other channels within a device. It’s a fact of life when dealing with electronics, but with thoughtful layout of a PCB or appropriate shielding on cables, it can be kept to a negligible amount.

##### Phase

In audio, the term phase refers to the relationship in time between two tones of the same frequency. To understand what phase it, first, let’s take a closer look at a sine wave.