Sound and Signal Flow

Question 1

MP: Discuss propagation of sound

Answer 1

The movement of sound through a medium. Sound moves through different mediums (e.g. water, air) at different speeds. Our sense of ‘space’ is based on propagation.

Question 2

MP: How much is the speed of sound?

Answer 2

340m/sec

1km/3 sec

Question 3

MP: What determines the speed of sound?

Answer 3

The speed of sound is determined by the properties of the air, and not by the frequency or amplitude of the sound.

Question 4

MP: The behavior of sound propagation is generally affected by three things:

Answer 4

• A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium.
• The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported.
• The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

Question 5

MP: Why is sound a longitudinal wave?

Answer 5

Because the direction of vibration is parallel to the direction it propagates. Think of a spring (a slinky) that you push on. (in contrast to a string of a guitar where it vibrates from left to right (a transverse wave))

Question 6

MP: What is the amplitude of sound?

Answer 6

How much the air compresses and rarefies as a wave form moves or propagates through the air. If we think of a spring (slinky) we push slightly on, it has a low amplitude. If we push hard on the spring, it has a high amplitude.
We perceive amplitude as loudness. The higher the amplitude, the louder.

Question 7

MP: How do you diagram, visualize a longitudinal wave?

Answer 7

we diagram it as it it’s transverse. But we need to know when we’re thinking about air that it is longitudinal compression and rarefaction.

Question 8

MP: What is the measure of amplitude? Give the two representations.

Answer 8

Decibels. It is a relative measure, There’s no definite set point where zero is, and it gets used differently in a variety of contexts.
Measured in the air: dBSPL (Decibels of Sound Pressure Level), the SPL portion is actually setting where zero is. dBSPL is related to the threshold of hearing (the quietest thing we can hear)
In the digital domain we measure amplitude with DBFS or full scale. This is related to the loudest thing that could be represented in numbers within the computer. (starts at loudest, goes negative from there)

Question 9

MP: What is the difference between amplitude and loudness?

Answer 9

Amplitude is something measurable by the computer, and loudness is our perception of that.

Question 10

MP: What is the dynamic range of a piece of gear?

Answer 10

its the range levels between the noise floor or the quietest that is just going to be the hiss that the device is putting, And the distortion when you get so loud that it just can’t reproduce it. And it gives you an ugly crackling or upper harmonics are added to the signal.

Question 11

MP: What is the dynamic range of a piece of music?

Answer 11

The range from its quietest section to its loudest.

Question 12

MP: What is the difference between frequency and pitch

Answer 12

Frequency is something that a computer can measure, pitch is something we perceive.

Question 13

MP: What is the frequency in sound?

Answer 13

Frequency is our sense of high pitch and low pitch. It is how fast the sound is vibrating. (e.g. a spring with pulses)

Question 14

MP: What is the timbre of a sound?

Answer 14

The collection of sound in multiple frequencies.

Question 15

MP: Give an example of sound at a single frequency.

Answer 15

The sine wave.

Question 16

MP: What is the range of human hearing?

Answer 16

20 Hertz => 20.000 Hertz

Question 17

MP: What is the measure of frequency.

Answer 17

The Hertz. 1 Hertz means one (vibration) per second.

Question 18

MP: What is the frequency response curve?

Answer 18

You hear different across the range of frequencies. How you hear them is visualized in a response curve. Every piece of gear also has a response curve. Thus the piece of gear (or your ears) act like an EQ (equalizer).

Question 19

MP: How can you visualize sound?

Answer 19

• An oscilloscope: Displays a waveform. up & down is amplitude; horizontal is time. It’s representing the compression rarefaction of sound. And that wave form is actually the exact path that the speaker’s going to make when sound is eventually made in the air by the speaker.
• A spectrum analyzer: Displays the frequencies of a sound on the horizontal axis, and the amplitude on the vertical axis.
• A spectrogram analysis: a spectrum analyzer repeated over time. This way you get the full view.

Question 20

MP: Any periodic waveform, like a sawtooth waveform, is going to have peaks at a number of frequencies. Which ones? What is this called.

Answer 20

Each of these frequencies is an integer multiple of the fundamental frequency.
This is called the harmonic series.

Question 21

MP: What is a transducer? How does a microphone transduce?

Answer 21

Converts from one energy type to another, and tries to do that without changing the signal at all.
A microphone converts pressure variations in the air, to voltage variations in a wire.

Question 22

MP: What are the two main microphone types.

Answer 22

• Condenser mics. Picks up all sound, very accurately. needs external (phantom) power.
• Dynamic mics. Picks up small range of sound. Doesn’t need external power.

Question 23

MP: When would you choose a dynamic mic?

Answer 23

On stage, in a loud environment. Because it does not pick up sound outside it’s small range. It’s also very rugged.

Question 24

MP: When would you use a condenser mic?

Answer 24

In a studio environment. It picks up everything with a very good sound quality.

Question 25

MP: Why is frequency response of a microphone important?

Answer 25

Because specific microphones target specific instruments. E.g. a voice mic. And frequency response is the way this is achieved. (e.g. for voice boost freqs in the 5k range.)

Question 26

MP: What is the polar pattern of a microphone?

Answer 26

What area around the mic it picks up well, and what area it rejects.

e. g. a cardioid polar pattern (only pick up the sound in front of the mic).
e. g. a omni polar pattern. (pick up everything, including the sound of the room).

Question 27

MP: What is the most import thing when recording with a mic.

Answer 27

The placement of the mic.

Question 28

MP: Where do you place a microphone?

Answer 28

Where it sounds the best. Walk around and listen…

Question 29

MP: What is the line level?

Answer 29

The audio level, the specified strength where all the different instruments communicate at. One of the major roles of an audio interface, a mic pre-amp, an amplifier is to raise (or lower) the signal to this line level.

Question 30

MP: What are the two different line levels?

Answer 30

+4: The studio standard line level.
-10: The consumer level.
These are gain stages, stages where you amplify or attenuate the sound.

Question 31

MP: Line level: what is unity?

Answer 31

A level where the sound is not amplified nor attenuated.

Question 32

MP: Why do you wanna use balanced cables?

Answer 32

Because they reject noise that is introduced through cable length and other factors. Thus balanced cables can be much longer then unbalanced cables.

Question 33

MP: How do you go from an unbalanced, to a balanced cable?

Answer 33

Use a direct box.

Question 34

MP: What happens in an analog to digital converter?

Answer 34

Sampling: measuring the continuous analog signal periodically and saving it as bits.

Question 35

MP: if you wanna connect a guitar to your audio interface, what do you need?

Answer 35

Instrument input/ direct input / Hi-Z input / High Impedance input.