Lesson One - 25th March 2013 - Posted on 2013-03-28 by Danielle Jardine

I went to the studio to meet with my mentor for the first time on Monday the 25th of March. I was excited to finally be starting the recording program. We discussed:

1. Sound Waves and their relation to Frequency -

• Sound waves are sine waves which are periodic, the inverse of the period is called the frequency.
• Frequency is the number of complete cycles (or complete periods) a sound wave can complete in a given amount of time. Hertz = Hz = cycles per second
  • Frequency Response =the range of frequencies that and audio system transmits within a level range.
  • Frequency Response Curves - are graphical representations of the freq response measured:
    • freq - logarithmic scale on the x - axis
    • amplitude - in dB or the y - axis

2. Wavelength, Waveform, and Phase -

• Wavelength is the distance from a particular point on a wave (sound wave) to the same point on the next wave.
• Waveform is the graphical representation of a signal; of its amplitude vs. time at a given instant.
• Phase is how far along in its cycle a waveform is.
  • If you have two identical signals 180° 'out of phase' with respect to each other they will both be canceled out.
  • 'out of phase' = two identical sound waves of the same frequency and amplitude but one is delayed slightly.
  • 'in-phase' = two similar sound waves of same frequency, shape , and peak amplitude are added the resultant sound wave is equal to that of the original but twice the original peak amplitude. 

3. Velocity and Pitch -

• Velocity is how fast or slow sound travels through a given medium. Depending on the density of the medium, sound may travel faster or slower.
• Pitch - is whether a sound is perceived as high or low, which is determined by the sounds frequency (the lower the freq the lower the pitch, the high the freq the higher the pitch).
  • humans hear from 20Hz - 20,000Hz
  • the initial vibration of a sound is called the Fundamental Frequency, which is the lowest pitch of a sound, it is also the strongest pitch we hear. Most sounds are made up of Fundamental Freq's and Overtones (Harmonics). When these are added to the Fundamental Freq the character of the music changes = timbre.
  • Lower Harmonics control the Timbre, Higher Harmonics control the harshness of the sound.

4. Sound Intensity, Equal Loudness, and Locate Direction (Binaural Localization) -

• Sound Intensity - Loudness = intensity. The intensity of a wave depends on the amplitude of the wave.
  • we don't perceive loudness as proportional to intensity, a sound wave has to be about ten times the intensity.
  • we measure sound intensity using a logarithmic scale, decibel (dB)
    • the threshold of hearing is 0dB
    • the decibel = one tenth of a bel
    • bel is named after Alexander Graham Bell
    • dB always requires a reference which is why we append a letter after dB such as dB SPL (sound pressure level)
• Equal Loudness - the human ear is a nonlinear device, all signal levels don't have the same input and output amplitudes which introduces harmonic distortion.
  • Harmonic distortion is the production of harmonics that do not exist in the original signal.
  • The Fletcher-Munson Equal-Loudness contours = The ear is most sensitive to sounds in the 3kHz to 4kHz range, so frequencies above and below 3 - 4 kHz must be a bit louder to be perceived as loud.
  • Its from these cuves that the optimum listening level of 85 dbSPL was established
  • Another effect experienced by a human listener is the interaction of tones with one another. Three situations can occur:
  1. Beats - two tones that are separated only slightly and have approximately the same amplitude will produce beats, equal to the difference between the two freqs.
  2. Combination Tones - the sound of two loud tones that differ by more the 50Hz, are interpreted by the ear as complex tones that include the two original sounds and an additional set of tones that equal the sum and diff of the two original tones.
  3. Masking - the phenomenon which prevents the ear from hearing softer sounds underneath loud tones.
• Locate Direction - the ability to use the two ears to determine from where a sound source appears also known as Binaural localization.
  • Inter-Aural intensity Difference - middle and high freq sounds originating from the human's left side will reach the left ear at a higher intensity (volume) then the right ear, causing a difference in intensities at each ear.
    • reflected sounds have to travel farther and lose energy from the source, to the reflector, to the ear thus reducing the intensity of the sound as perceived by the right ear and the brain tells us that  the sound originated from the left side.
  • Inner-Aural Arrival-Time Differences - At lower frequencies the ear uses time delay - the short but significant delay of frequencies between the left and right ear - to determine which sound arrived first.
  • Pinnae of the Ears - the pinnae uses the shape of the ears and the strange bumps and ridges to reflect the sound into the ear. These ridges introduce light time delays between the direct sound and the reflect sound. This time delay is a function of the angle of incidence: at what angle is sound bounced off the pinnae.

5. Attack, Decay, Sustain, and Release -

• Over time the loudness and spectral content of sound changes over time. This change veries from instrument to instrument. Sound synthesis techniques often use an envelope generator that controls the parameters of any given sound at any point in its duration; this is usually an 'ADSR' envelope. ADSR =

• Attack = time taken to go from nothing to peak, beginning when the key is first pressed.
• Decay = time taken for the sound to come down from the attack level to the sustained level.
• Sustain = the level during the main duration of the sound, up-until the key is released
• Release = time taken for the level to decay from the sustained level to zero after the key is released.

We prepared for the next chapter which is Digital Recording. We discussed a bit about sampling and bit depth. Tomorrow I go into the studio for my first recording session. It will most be me watching how Zack sets up for the recording session though it would be awesome if I am able to help out a bit. I'm going to take notes on questions that I have so I can address them on Monday when I go in for my Digital Recording lesson...lots of reading to do between then and now.