# Frequency Charts

Hey folks

Just curious as to the reason they graph out frequency charts as they do. What im refferring to is the fact that they Display 20 - 100hz on the first 1/4 of the chart, then 100hz to 1khz on the 2nd quarter, followed byu the 1k-10k, and lastly the 10-20k, meaning they graph out half of the hearing range in the last 1/4

i guess this is a kind of a dumb question, it just seems that by reading the first half of the graph covers just 1/20th of the range while the other 19/20th's are all crammed together.

i know that it would be pretty difficult to put a graph in a magazine of 20,000 without using some technique to compact it. Is there any logical reason that group it out the way they do other than to save space?
slappy
9 responses
 12-15-2004 3:44amThat's just what log scales look like. The plots are variables which are exponents of a base of value ten. If you dump the base and exponents and just look at the value of the variables, the scale will be linear, e.g. (log)100 = 2, (log)1000 = 3."Is there any logical reason that group it out the way they do other than to save space?"No, you are right - its to save space. 12-15-2004 3:46amMusic is best looked at in terms of musical notes, not frequencies. Since an octave translates to a doubling of frequency the deep bass octave of 20Hz to 40Hz has the same number of notes as the high treble octave of 10kHz to 20kHz. The log graph better correlates to how humans actually hear music. Simply put, there are more musical notes in the lower frequencies. 12-15-2004 11:42amDitto, log scales closer approx how we perceive sound. like the difference between "white" noise and "pink noise." White noise is more or less equal energy (noise) over the entire range of frequencies, from say 20hz-20khz. So if you were to think of it as visible light, the even balance would appear to look "white." Even though white noise is even from 20-20k, it sounds like it has more excess high frequency noise than low freq. This matches our perceived hearing. It's balanced, but it doesn't sure sound that way! However, pink noise has more energy down low. So if you were to think of it as visible light, it would appear to look the color pink (redish). But pink noise to most humans, appears to "sound" even balanced over your entire hearing range. That's sort of oversimplifying it, but you get the itea. Well, that's at least how I understand it. Some of comparisons only make sense when charted on a log scale. Freq response as perceived by humans is one of them. 12-15-2004 1:58pmOnhwy is right. It's easy if you look at the piano. Each octave doubles the frequency. Middle C is 260 Hz. One octave up is 520, the next octave is 1040. So if you were to mark all the 'C's on the piano on a log scale they would be evenly spaced. 12-15-2004 7:43pmAllright!Thanks guys! 12-15-2004 11:14pmIn what cases would you chose Pink noise or White noise for testing?Rives, help me out. What note is 440 Hz? I thought that was middle "C"? (As you can tell, I don't play a musical instrument!) 12-16-2004 11:53amFatparrot, 440Hz is an A4. Note that A5 has a frequency of 880Hz, thus it is one octive higher than an A4 since it has twice the frequency. You can see this on the log graph as you go up an octive the spacing of the frequency gets closer together because 1) twice the frequency, 2) shorter wavelengths, also the same notes octives apart will be equally spaced on the graph. FYI middle C which is C4 has an frequency of 261.63Hz. 12-16-2004 2:22pmSlappy:Set up a graph where the differences between each whole number is one inch. The difference between 1 and 2 would be one inch and the difference is one hundred percent(2 doubling one). The difference between 10 and 11 would be ten percent but still one inch. From 100 to 101 would be one percent but still one inch.Semi-log graph paper puts the horizontal lines closer together the higher the lines are so the distances and percentages are logical both ways.The kid at the stationary store who did his/her math homework can find the semi-log graph paper for you. 12-17-2004 5:25amPerhaps surprisingly, there is considerably more variation to note/frequency assignment--continuing even today--than one may have initially imagined. See, for example http://www.uk-piano.org/history/pitch.htmland http://hypertextbook.com/facts/2003/DanielleDaly.shtml.