Answer each question to the best of your ability. You may use a calculator and/or any reference materials. Please show all work - partial credit may be awarded. Answer all questions using specified units when applicable.
1. Study the gain structure below and show the signal level at each stage. Show all calculations.
2. Signal A has an amplitude four times greater than signal B. Using the formula given, express the ratio of signal A to signal B in decibels.
LeveldB = 20 log (v1 / v2)
3. Black Box
An audio device has three variable controls, three audio signal level meters, two switches, and three jacks. The device exhibits the following behaviors:
a. The level of a signal inserted to jack A is modified by controls 1 and 3, and is observed at jack C and meters 1 and 3 when switch 1 is activated.
b. The level of a signal inserted to jack B is modified by controls 2 and 3, and is observed at jack C and meters 2 and 3 when switch 2 is activated.
c. When switch 1 is not activated, the signal from jack A is no longer present at jack C or meter 3.
d. When switch 2 is not activated, the signal from jack B is no longer present at jack C or meter 3.
e. When signals are inserted at both jacks A and B, a combination of these signals is observed at meter 3 and jack C in accordance with conditions a-d.
Draw a flow chart (block diagram) of this device. Indicate the function of each component. What is the most likely function of this device?
Jack A________________ Jack B________________ Jack C________________
Control 1______________ Control 2_____________ Control 3______________
Meter 1_______________ Meter 2_______________ Meter 3_______________
Switch 1¬_________________ Switch 2¬_________________
4. The block diagram below describes the signal flow within a digital delay device. The user operates the device via seven rotary controls, labeled A through G. Delay is provided by the module labeled t. The LFO is a low frequency oscillator that generates a sine wave, which can be used to continuously increase and decrease the delay time.
a. Which level control should be used to adjust the output level from the device? Explain.
b. How would you adjust the balance between the delayed signal and the non-delayed signal? Explain.
c. Which controls affect the audio signal level? Explain
d. Which control should you adjust to set a fixed (nonvarying) delay time? Explain.
e. Which control adjusts the frequency of the LFO? Explain.
5. Express the following measurements in a single graph:
1. An audio signal with a frequency of 1 kHz has a certain reference level.
2. An audio signal with a frequency of 5 kHz has a level 4 units greater than the level at 1 kHz.
3. An audio signal with a frequency of 10 kHz has a level 2 units greater than the level at 1 kHz.
4. An audio signal with a frequency of 15 kHz has a level 3 1/2 units less than the level at 1 kHz.
5. An audio signal with a frequency of 50 Hz has a level 12 units less than the level at 1 kHz.
6. An audio signal with a frequency of 100 Hz has a level 1 unit greater than the level at 1 kHz.
7. An audio signal with a frequency of 500 Hz has a level 2 units less than the level at 1 kHz.
6. The waveforms below are examples of standard square and sawtooth waves.
a. What is the frequency of the sawtooth wave?
b. The frequency of the square wave is exactly twice the frequency of the sawtooth wave. Label the appropriate units on the time axis above.
c. Is the RMS value of the square waveform greater than, equal to, or less than the RMS value of the sawtooth wave? Explain.
Extra Credit: Draw a composite waveform equal to the sum of the two.
7. Fill in the blanks relating to the graph below. (Reminder: Show your work!)
The height of the wave along the “Volts” axis is called the , and for the waveform pictured above is a total of volts, or volts peak-to-peak, or volts RMS (hint: review relationship between peak and RMS voltage for a sine wave). This parameter is musically perceived as the ____________ of the note.
The time length of one repetition or cycle of a repeating waveform along the time axis is called the ________. This is mathematically related to the , which is expressed in “cycles per second” or ______ . That relationship is the following: .
The “cycles per second” of the waveform pictured above is ________. This parameter is musically perceived as the ________ of the note.
The distance length of one cycle is called the . This is mathematically related to the as follows: . For the wave pictured above, this distance is (assume speed of sound = 1100 ft/sec) .
The shape of a waveform is determined by the _______ content. Musically, this is perceived as . The shape of the waveform pictured above is a ________ wave, which is made up of
Any signal or waveform whose cycles repeat exactly can be called , which means we will perceive it as having a .
a. What is the frequency of this waveform?
b. The above input signal is sent through an audio device whose frequency response is given below. What would be the resulting RMS level of the signal at the OUTPUT of the device, expressed in dBu.
31.5 63 125 250 500 1k 2k 4k 8k 16k
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