2. A BRIEF OVERVIEW OF THE SCIENCES OF SOUND Intro to Sound Part 2 1

3. Echo and Reverberation Echo – a discrete reflection of a sound...it is intelligible Reverberation – a “cloud” of reflections that are indistinguishable (Holman)  A little bit of reverb creates a “bloom that subtly reinforces words and notes” (Cox)...but too much reverb makes sounds unintelligible “Echo and Reverb” video (1:16) “Echo and Reverb” 2

4. Inverse Square Law 3 Source: http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/invsqs.html

5. The Inverse Square Law 4

6. Image from Howard & Angus (2009) 5

7. Boundaries Image from Howard & Angus (2009) 6

8. Influences on Sound Propagation (see Holman Ch. 1) Source radiation pattern Absorption Reflection Diffraction Refraction Constructive and Destructive Interference and Beating Doppler Shift 7

9. Break NOTE: Slides that follow are adapted from Rick Pitchford’s COM 353 slides. 8

10. Waveform Clipping: Transfer Characteristics of all amplifiers are “S” shaped, curved and flattened at the ends, distorting the output signal if the input is too large. Amplifiers are meant to be used in their linear range to avoid distortion. (When you “go to 11” this may involve distortion!) Maximum Positive Output Maximum Negative Output

11. Gain Compression: unity gain 2:1 gain ratio 4:1 gain ratio knee threshold Automatic Gain Control allows the dynamic range of a signal to be reduced. This can be used to maximize signal intensity while preventing signal overloads. As the input signal level passes a set threshold value, a knee is encountered in the transfer characteristic. Beyond the knee, the gain of the amplifier is lower. --  GOOD: Speaking  BAD: Symphonic orchestra  There is also gain expansion  NOT the same as BRR compression!

12. Microphone Frequency Response: (X = frequency, Y = amplitude) Shotgun, Dyn Desk, Omni, Dyn deciBels - 5dB per mark Lav, Omni, Cond Images from ElectroVoice Corp. documentation deciBels - 5dB per mark 20 100 1K 10K 20K 11

13. Frequency Equalization: Frequency equalization is achieved by passing a signal through an amplifier or passive component block with a variable frequency response: el-cheapo “tone” control: very limited high-frequency adjustment bass and treble controls: low and high frequency level adjustment graphic equalizers: placement of slider controls approximates the resultant frequency response parametric equalizers: sub-octave resolution and ability to fine-tune the amplitude of each individual frequency band Frequency Output Level Frequency Output Level Frequency

14. Output level Input Signal The Goal of EQ: Change a signal with a sub-standard spectral balance or frequency response by sending it through an amplifier with a variable frequency response. The output signal has a reshaped, hopefully improved, frequency response. Frequency Output Level Result Frequency Output Level EQ Block

15. EQ can be used to “flatten” a signal with poor frequency response EQ can correct a signal with “path problems” (e.g., long lines = high freq roll-off; recorded on tape) EQ can be used for effect (AM radio sound, telephone, etc.) or sweetening (boosting low and/or high frequencies) In all cases, don’t over-do it; Less is More EQ Examples: sound files from http://www.dougyoungguitar.com/eq_pickuptest.htm Flat, as recorded Bass Boosted Mid Boosted Highs Boosted Telephone“Good” EQ

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