0

I have been learning to play guitar, and I wanted to look at it from a more physical point of view, because that is something I like to do. Maybe a similar question has been asked here, but I could not find it. If this has already been asked, and if you have the link, please share.

What is the similarity between the frequencies 130.81Hz (C3) and 261.63 (C4), with standard reference as A4 = 440Hz, that makes us call both the frequencies as C? Why do they sound similar? Say I played both the Cs together in unison while playing fingerstyle, it sounds good, and they resonate really well, but when played separately they do sound different. Why is that?

6
  • 2
    Does this answer your question? What is an octave?. In particular, a comment refers to the Wikipedia page for octave, which may answer your question.
    – Aaron
    Oct 19, 2020 at 6:38
  • Note that 130.81*2 = 261.63 (or refer to @Aaron 's comment).
    – Tom
    Oct 19, 2020 at 6:56
  • @Aaron Thanks that helped, also thanks for the answer, just a follow-up question, like the first answer in the link you gave said, the octaves sound similar in our brains, so is it also possible for colors in the visible spectrum to repeat themselves, I know this is going in the physical realm now leaving behind the music but in case you know that might help me more in understanding.
    – naruto_022
    Oct 19, 2020 at 15:20
  • @naruto_022 I don't know whether sound waves and electromagnetic waves can be compared in that way, but consider the "color wheel", which demonstrates how one color blends into the next in a way that forms a loop.
    – Aaron
    Oct 19, 2020 at 15:27
  • 1
    @naruto_022 The properties of instrumental sounds are the properties of a "standing wave". Light through an appropriate medium (discussed in the article) might work as you're looing for.
    – Aaron
    Oct 19, 2020 at 15:49

2 Answers 2

0

The frequency of C4 is (or should be) exactly twice that of C3. We call both of them C, as they do sound similar. The simple fact is that contained in most sounds are harmonics. That is, other pitches which are related to the original pitch.

The first harmonic, moving up to higher notes, is the octave (which for C3 is C4). The next is an octave and a fifth, making P5 above that octave note - whatever the original happens to be - here, C3, producing note G4. The next audible harmonic is another C, C5.

So, C3 also produces C4 and C5, whereas C4 also produces C5 (which has a Hz of double C4).

Some instruments produce stronger harmonics, which gives them their particular timbre.

0

An ideal vibrating string (for example) vibrates not only at its full length but also half its length, 1/3 its length, 1/4 its length, etc. This produces what is called the harmonic series -- the same series one learns about in math or physics classes.

In the OP example, an ideal guitar string vibrating at 130.815Hz would also be vibrating at 261.63Hz. Thus, C3 "contains" C4. The sounds meld so well that we have come to consider them "the same note", even though one is clearly higher/lower than the other.

As an aside, it is common in ear-training classes for students to have difficulty distinguishing octaves (2:1 ratio) from fifths (3:1 ratio -- or, really, 3:2 octave adjusted). These are the two "closest" sounds to the fundamental within the harmonic series.

The science of fully understanding the answer to your question and ones like it is acoustics, which studies sound, along with psychoacoustics, which studies how the brain processes sound.

2
  • I'd say that an open string vibrating at say 100Hz also vibrates at 200Hz, but would an open string vibrating at 200Hz also vibrate at 100Hz? True about the P5 - someone singing out of tune will often be that 'half an octave' out.
    – Tim
    Oct 19, 2020 at 11:43
  • @Tim Thanks. I have a penchant for getting that backwards -- much like my newfound penchant for typing "it's" instead of "its". So, double-thanks;
    – Aaron
    Oct 19, 2020 at 15:19

Not the answer you're looking for? Browse other questions tagged or ask your own question.