Spectrum log(f) LEGENDA

Special Interest Groups Audio Processing
1

Hey All.

I would like to know if there is a legenda for the spectrum log visualisation mode. In other words, what does the range of colours mean in terms of sound, frequency, dB, et cetera? Is there any hard data on this?

Regards, Jelle

2

Frequency is on the vertical scale.

Colour is allocated according to the audio level at any particular frequency.
(low level) Blue > Purple > Red > White (high level)

The scale is not fixed, but is set in Preferences.
For Audacity 1.3.9
Edit > Preferences > Spectrograms

You will see there is also an option to display “Greyscale” - This gives you:
(low level) No colour > grey > black (high level)

3

Thanks for the quixk reply Steve!

So you are saying that there is no scale n terms of dB-ranges that belong to a certain color? Can I assume tat those 4 ranges of audio level (blue, purple, red,white) are devided into identical parts?

And then another question: What the difference is between the ‘spectrum’ and the ‘spectrum log(f)’ mode? Is the one linear, and the second logaritmic distributed?

Best, Jelle

4

Yes. You can see this when you switch views - the vertical scale on the left changes from linear to log.

– Bill

5

The plain spectrum tells you that for any one sample of the song, the following frequencies were present. It doesn’t tell you exactly when.

This is the spectrum of me pressing the “G” key on my piano. It represents all the energy during the entire key press.

http://kozco.com/tech/audacity/piano_G1.jpg

This display does tell us loudness up and down and pitch side to side accurately. You would want the logarithmic frequency scale to make up the difference between the mathematics and our ears. Half-way up the frequency range is obviously about 10,000 Hz, but any human will tell you a middle tone is about 400Hz. A 440 is the oboe tone at the beginning of the orchestra. 400Hz is one of the two common broadcast test tones. The arithmetic is linear and the musicians log. Same music.

The ear works the same way with loudness. Half audio level is clearly -6dB on any voltmeter, but people hear half volume at about -18dB.

I’m never used that display, but it appears to tell us frequency distribution up and down against the performance time side to side There are no other ways to display data, so the loudness is relegated to colors.

I would be using this display to tell me when in the orchestra performance the area of interest is, and then use the spectrum – log to tell me more accurate information about that note or phrase.

Koz