Intro to Sound Practice Exam notes

Question

Answer

"How do you calculate wavelength?"

"Wavelength = Speed of Sound ÷ Frequency (λ = ν/f)"

"How do you calculate period?"

"Period = 1 ÷ Frequency (T = 1/f)"

"What is the formula for speed of sound at different temperatures?"

"Speed of sound = 331.4 + (0.6 × Temperature°C)"

"What is simple harmonic motion?"

"A system that vibrates at a constant frequency

"What happens when two sine waves of the same frequency and amplitude are played 180° out of phase?"

"They completely cancel each other out (destructive interference)"

"What is beating and when does it occur?"

"Beating occurs when two frequencies differ by only a few Hertz. The beat frequency equals the difference between the two frequencies."

"What is comb filtering?"

"Occurs when a signal is combined with a delayed version of itself (e.g.

"What are the four parts of an ADSR envelope?"

"Attack - How quickly sound rises to maximum volume; Decay - Initial decay after the transient; Sustain - The holding of the note; Release - The decay of the note"

"How do we perceive the direction of sound?"

"Two ways: Interaural Intensity Differences (IID) - Volume differences between ears (for high frequencies); Interaural Timing Differences (ITD) - Timing differences between ears (for low frequencies)"

"What is an SPL meter and what does A-weighting mean?"

"A device that measures sound pressure level. A-weighting applies a high-pass filter

"What is the Haas Effect (Precedence Effect)?"

"When copies of the same sound arrive from different directions

"What is the threshold parameter on a compressor?"

"The signal level required to make the compressor engage and reduce gain. Below threshold = no compression; above threshold = gain reduction."

"What does an expander do?"

"A dynamic processor that reduces the volume of signals below the threshold by a predetermined ratio. Opposite of a compressor."

"What are the four types of dynamic processors?"

"Limiters - Severely reduce gain above threshold; Compressors - Gently reduce gain above threshold; Expanders - Gently reduce gain below threshold; Gates - Severely reduce gain below threshold"

"What is a low pass filter?"

"An EQ filter that allows low frequencies to pass through while attenuating (reducing) higher frequencies."

"What is a high pass filter?"

"An EQ filter that allows high frequencies to pass through while attenuating (reducing) lower frequencies."

"What is convolution reverb vs algorithmic reverb?"

"Convolution - Uses recorded impulse responses of real spaces; CPU intensive but very realistic; Algorithmic - Computer simulation; more control and creative possibilities but less realistic"

"What does the dampening parameter do in reverb?"

"Dampening reduces the reverb time of higher frequencies

"Why might a room have longer reverb time for low frequencies?"

"Thin acoustic foam reduces high frequencies but has little effect on low frequencies

"How does sample rate relate to Nyquist frequency?"

"The highest recordable frequency is ½ the sample rate (Nyquist frequency)."

"How do you calculate dynamic range of a digital system?"

"Dynamic Range = Bit Depth × 6dB per bit"

"What's the difference between 24-bit and 8-bit audio?"

"8-bit has a much higher noise floor due to quantization distortion - you'll hear more 'hiss.' 24-bit has a noise floor too low to hear under normal conditions."

"What are three ways digital audio can be transferred?"

"Electrically (cables - USB

"What sample rate is used for sound-to-picture work?"

"48kHz (used for TV

"What sample rate is used for CD audio?"

"44.1kHz"

"What is the Doppler Effect?"

"The change in pitch when a sound source moves relative to the listener. Approaching source = higher pitch (shorter wavelengths); receding source = lower pitch (longer wavelengths)."

"What is white noise?"

"Random frequencies with equal energy per bandwidth. Sounds 'hissy' with little bass. Appears flat on FFT analyzer."

Pink Noise

Random frequencies with equal energy per octave. Lows and highs sound equally loud. Appears flat on RTA analyzer. Better represents musical signals.

"What are the essential formulas to remember?"

"Wavelength: λ = ν/f (λ = 344/frequency); Period: T = 1/f; Frequency: f = ν/λ or f = 1/T; Speed of Sound: ν = 331.4 + (0.6 × °C); Dynamic Range: Bit depth × 6dB; Nyquist Frequency: Sample rate ÷ 2"

"What are the key human hearing specifications?"

"Frequency Range: 20Hz - 20kHz; Dynamic Range: 0dB - 120dB SPL; Most Sensitive: 3-4kHz; Minimum Threshold: 20 microPascals (0dB SPL); 6dB increase = doubling of pressure; 10dB increase = perceived as 'twice as loud'"