Frequency

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I am teaching a basic overview of what audio frequency is and how it relates to pitch, timbre, and perceived loudness.

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Frequency

  1. 1. FrequencySasha Vulovic
  2. 2. Introduction• My name is Sasha, I live in Detroit, Michigan. I’m from Seattle, lived in Tucson for a couple years and moved to Detroit a year and a half ago.• I’m not super familiar with music recording or any recording devices. I do play music.• I will be teaching a basic overview of frequency.• Thanks!
  3. 3. What Frequency Is• Frequency refers to the number of sound waves per second: measured in Hertz, number of cycles per second• Sound will travel at the same speed always, 340 meters per second or about 1/ 5 of a mile. But within that direction of sound there is the oscillation of each soundwave• - like ocean waves, one cycle would be measured from wave peak to wave peak- but unlike ocean waves, sound waves oscillate IN the direction they are moving.
  4. 4. Not Identical to Pitch!• Just as amplitude can be said to be the quantitative measure that affects our perception of loudness, so frequency is the quantitative measure that affects our perception of pitch.• Amplitude is not loudness, frequency is not pitch, but they affect those audio perceptions.
  5. 5. Our Hearing Range• Our hearing range extends from a low frequency of 20 Hertz (20 soundwaves per second) to a high frequency of 20,000 Hertz. As adults due to worsened hearing over time and exposure to noise, the highest frequency we can hear is more often 18,000 to 19,000 hertz.• The higher the frequency, the higher the pitch we perceive it to be.
  6. 6. Notes emit more than one frequency.. Recognize the fundamental• What is interesting is that despite our being able to name the pitch of a sound- say middle C- it is very rare that the frequency corresponding to the middle C pitch is the only one emitted in the sound. Most instruments, voices, and objects that create sounds we perceive to be of one pitch, are actually emitting several frequencies.• A tuner, on the other hand, will have less variation in its frequency and emit simply the fundamental frequency: we call its waveform sinusoidal• .The frequency that corresponds to the pitch we recognize is usually the lowest one emitted, and it is called the fundamental frequency.
  7. 7. Harmonic Overtones• Often the multiple higher frequencies are in harmony with this fundamental; theyll be multiples of the fundamental frequency.• So say the fundamental frequency of a note played at middle C is 130 Hertz; other frequencies emitted could be 260 Hertz, 390 Hertz, 520 Hertz (all multiples of 130 Hertz).• Every time you double the frequency of a sound or note, the corresponding pitch is an octave higher.• So while there will be some frequencies of higher pitched Cs playing while the fundamental frequency is middle C, the note and pitch will still sound clean and on-key because the pitches are in harmony. Thus these overtone frequencies are called harmonics.
  8. 8. Inharmonic Overtones• Its not always the case that these overtone frequencies are multiples of the fundamental. So when its the case that you have higher frequencies than the fundamental being emitted that are not exact multiples, these will be “off- key” and are called inharmonic frequencies.• The overtone frequencies (higher than the fundamental) plus the fundamental frequency together are called partial frequencies or partials.
  9. 9. Timbre• Timbre is a tonal quality affected by the presence of multiple frequencies.• A tuner playing middle C sounds very different from an opera singer singing the note or a piano or a banjo• even the same note sung by the same person can emit different variations of frequencies, and thus contain different timbres, depending on the shape of the singers mouth as breath is pushed out.• An interesting experiment related to this was watching the visual representations of audio frequency vary as our teacher sang different vowels all at the same frequency:• I and O emit higher overtone frequencies than A or E though we would all recognize the fundamental frequency and thus pitch as being the same throughout. Its an interesting phenomenon to keep in mind for music or even speech- how different words, peoples names, sung or spoken affect the tonal qualities our listeners perceive..
  10. 10. Frequency affecting Perceived Loudness• Though we hear well enough the overtone frequencies to differentiate between the tones of different instruments or tuners playing the same note, we dont hear very high- or very low- frequencies as WELL.• Our range of hearing does stop at about 20 Hertz in the low range and 20,000 Hertz in the high range but it does not stop abruptly; frequencies of 15,000 Hertz we would have more difficulty hearing than frequencies of 300 Hertz.• Thus, though frequency does not affect amplitude, it does affect our perceived loudness.
  11. 11. Equal Loudness Contour Curves• A frequency of 16,000 Hertz played at the same amplitude as a frequency of 300 Hertz, will sound less loud• Equal loudness contours are the visual graph describing this phenomenon.• Listeners were asked to adjust the volume of notes corresponding to a large range of frequencies so that the sounds they heard would be "equally loud." The earliest researchers to make a big project of this were Fletcher and Munson and thus these curves are often named after them but their experiments were less accurate than later ones.• What researchers did find was:• 1. To keep the level of perceived loudness the same across different frequencies, the amplitude of higher and lower frequencies needed to be greater and greater, than the lower amplitudes of frequencies right in the middle of our hearing range• 2. Each person had their own variations even within that general pattern. The frequency corresponding to a pitch of F# might sound a lot louder to me, played at the same amplitude as G, than it would to you, as an example.

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