Frequency response is the measure of a sound card's ability to handle music without changing the relative loudness of sounds of various pitches. Errors in frequency response is generally thought to be the most audible form of Linear Distortion. Frequency Response is a means of characterizing one form of Linear Distortion.
Frequency response is specified by the combination of three or four numbers.
The wider the range of frequencies for a given tolerance, the less Linear Distortion the card has. Regions of raised or depressed response that cover a wider range are easier to hear. While not shown in the graph, narrow dips are generally thought to be less audible than narrow peaks. If the program material does not contain frequencies that are affected by such peaks and dips as exist, then the peaks and dips will have very little audible consequence. If other components in the system have significant frequency response variations, then smaller variations in the more accurate components may be harder to hear.