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FREQUENCY RESPONSE CURVES


A single wave goes up and down a certain number of times per second (FREQUENCY).  The amount of a particular frequency that exists in a sound can be measures on a device called an OSCILLISCOPE.  The overall pattern of peaks and valleys seen on an oscilloscope is the sound’s FREQUENCY RESPONSE CURVE, which is a line on a graph that charts frequency (Hz) along the bottom from left to right, and sound strength (measured in Decibels or dB).  This graph and line is similar to a graphic Histogram, which charts the concentration of dark, midtone, and bright pixels in an image.

The Frequency Response Curve of a simple sine wave will be a lone peak at the sine wave’s frequency.  Once you start combining even simple sine waves you start to get more peaks and even peaks that start to push each other’s shapes.  The Frequency Response Curve will be higher where there is a greater amount of sound at a particular frequency, and lower where there is not much of a particular frequency.

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This image (copyright Shure) is the frequency response curve for a Shure SM94 microphone.  The curve shows that the microphone dips above 10,000 Hz (10 kHz) and below 200 Hz.  While this microphone would be well suited for most instruments, it would not be the best choice for bass (which has important sounds below 200 Hz) or cymbals (which has important sounds above 10 kHz).

 

           
Low sounds such as a low muffled rumble or the lowest notes on certain instruments are called BASS.  High sounds such as a cymbal or the “ss” sounds of human speech are called TREBLE.  Middle sounds that are in between Bass and Treble are called MIDRANGE.

While the exact points where a sound crosses over from one type of sound to another is debated, Sounds below 200-300 Hz (cycles per second) tend to be considered BASS frequencies, and sounds above 5K-7K Hz (5,000-7,000 cycles per second) are considered TREBLE.  All the sounds in between are considered MIDRANGE.

Parts of human speech that make up certain important sounds use High Frequencies, such as D, T, S and Z.  As people age or suffer hearing damage, they lose sensitivity to high frequencies and the ability to hear speech as clearly.

All sound has a frequency response curve, which is a curved line that shows the amount of low to high sound energy distribution.  Many musical styles have evolved along with sounds that have become strongly associated with them.   For example, a bassy reggae song may have frequency response curve that looks completely different than that of a bright and edgy punk rock song.  Throughout the years different musical sounds have been blended, so there is somewhat less sonic distinction between musical styles than there used to be.