32.70Hz or 33Hz in ohms or uF?

Discussion in 'The Projects Forum' started by PandaHero23, Jul 1, 2016.

1. PandaHero23 Thread Starter New Member

Jun 16, 2016
19
2
I found a chart of musical notes in frequency and according to it, C1 is 32.70Hz. So with an oscillator, what value resistor and/or capacitor would i need to get it to oscillate at 32.70Hz or 33Hz?

2. Papabravo Expert

Feb 24, 2006
10,338
1,850
The problem as stated does not have a unique solution. In order to tackle the problem we need to see a schematic of the oscillator. We are not limited to resistors and capacitors, but

For a given resistor we can compute a capacitor, and for a given capacitor we can compute a resistor.

3. Veracohr Well-Known Member

Jan 3, 2011
559
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To be more blunt: a resistor and capacitor will not oscillate by themselves. Oscillators include active components because oscillators require gain.

4. RichardO Well-Known Member

May 4, 2013
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Keep in mind that resistors and capacitors are not very accurate or stable over time and temperature. In addition, real components will never have the values calculated. For many cases these errors are not a problem.

For music, the correct frequency must be quite accurate and stable. Notes in the musical scale are only a few percent apart. If notes are played one at a time a small error can be tolerated (at least to my untrained ear). When more than note is played at the same time the frequency errors are much more apparent. This is because the notes beat against each other and create more frequencies.

I will stop here and let someone that has real musical knowledge explain things better.

5. BR-549 Well-Known Member

Sep 22, 2013
2,164
415
As others have said, you will need a good stable reference for music tones.

I could never understand how music people can say that C1 is 32.7 hz. There are many pitch standards.

I don't hear 32.7 hertz when I press that key. I hear a bunch of noise.....but it's all higher than 32.7 hertz.

Try out my handy dandy tinnitus checker to listen to a 32.7 hz. pure note.

You can also use this to beat out and determine your tinnitus frequency. OR your little friends voice.

http://www.szynalski.com/tone-generator/

6. MrChips Moderator

Oct 2, 2009
12,622
3,451
RicharO is correct. There are some subtleties about musical notes that are not recognized or understood by many people.

Off Topic

The musical scale is divided into octaves, i.e. doubling of frequencies.
For example,
A1 = 55 Hz
A2 = 110 Hz
A3 = 220 Hz
A4 = 440 Hz
A5 = 880 Hz

where A represents the musical note "A" or "la" as in "do-re-me-fa-so-la-ti-do"
and the numeral is the octave.

Each octave consists of twelve equally spaced notes (in the Western musical scale).
C C# D D# E F F# G G# A A# B

That is, the mathematical ratio between the frequencies of any two adjacent notes must be the same.
This ratio is 1.059463, which is the 12th root of 2:

$\frac{1}{\sqrt[12]{2}}$

Such a mathematical arrangement of musical notes is called "Equal Temperament Scale".

A triad consists of three notes in the scale. A major triad starting with "do" consists of
do - me - so.

In the scale of C, a C-major triad consists of C, E and G.
In order for these notes to "harmonize" and not create annoying "beats", the frequencies of each pair of notes must have an exact ratio of integers:

E/C = 6/5 = 1.25000
G/C = 3/2 = 1.50000

Another way of picturing this, an exact number of cycles of one note must fit into the same time span as another integer multiple of cycles of the second note. For example, 3 cycles of G-note has the same duration as 2 cycles of C-note to give "perfect harmony". This is called the "Just Scale".

Let us compare the equally tempered notes with the required notes for a Just Scale

E/C = 1.25992, compared with 1.25000
G/C = 1.49831, compared with 1.50000

Here are the actual frequencies. Compare the equally tempered scale with the just scale.
 Note Equal Temperament (Hz) Just Scale (Hz) Error (Hz) C4 261.63 261.63 1 E4 329.63 327.03 +2.60 G4 392.00 392.44 -0.44

Hence pre-tuned musical instruments such as pianos, keyboards and stringed instruments such as most guitars are compromises at best. A well trained musician playing a fretless instrument such as a violin, viola or acoustic bass is able to "tune" the note by ear and obtain the "exact" desired frequency.

You can tune an instrument to play perfect harmony in Just Temperament Scale for a given key, example C.
However, the notes would be in disharmony when playing a different triad.

Music is all about math and physics.

Reference: http://www.phy.mtu.edu/~suits/scales.html

7. Veracohr Well-Known Member

Jan 3, 2011
559
77
I read a book I found very interesting about the history of tuning systems and the eventual arrival at the 12-tone equal temperament system. To paraphrase, the author said all tuning systems previously had intervals that just sounded too bad to use, and the TET made everything except octaves equally bad but mildly enough that it's useable.

8. AnalogKid Distinguished Member

Aug 1, 2013
4,676
1,294
Which oscillator. With additional active components (transistors, opamp, logic gate, etc.) you can set a square wave oscillator frequency with one resistor and one capacitor, but it will not sound like a musical note. For a sine wave oscillator with no inductors, you need a minimum of 3 resistors, 2 capacitors, and a light bulb.

ak

9. hp1729 Well-Known Member

Nov 23, 2015
2,067
230
32.7is 99.09% of 33 so the resistor value needs to be appropriately smaller.

10. DickCappels Moderator

Aug 21, 2008
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Below is one solution. Pick an easy value for R and find C. C = 1/(1.4 x f x R). For 32.7 Hz and 10k the capacitor would be approxiamtely 2.2 uF.