final

audio tech

Name the 3 major microphone transducer types. hint: (D,C,R)

Dynamic, Condensor and Ribbon.

Describe how dynamic mics are constructed.

1. Thicker diaphragm

2. Composed of a voice coil, magnet, XLR socket, transformer and grid

Describe how condenser mics are constructed.

1. Thin diaphragm

2. Composed of a back plate and battery. Inside the battery is a resistor, potential source and a signal amplifier.

Describe how ribbon mics are constructed

1. Different diaphragm all together

2. Composed of a ribbon, magnet, output and transformer.

What would the size and thickness of a diaphragm change in a microphone?

Thinner diaphragms allow for a faster transient response, which is easier to pick up frequencies and details. (Condenser mics)

Thicker diaphragms are harder to vibrate and consequently have a slower transient response. (Dynamic mics)

What is the difference between pressure operated and pressure gradient capsules?

Pressure Operated capsules accept sound equally from every direction because the back of the capsule is not exposed to changes in pressure (equalized). They only react to air pressure - not direction. Whereas Pressure Gradient capsules have both sides of the diaphragm exposed to pressure variation, meaning it won't react to pressure from the side but only toward the capsule. Because both sides are exposed to pressure variation, it is known as a bidirectional polar pattern.

What decibel scale do we use for describing "gain" and "loss"?

We use the decibel system, a logarithmic scale (10 as the base). 0dB means there is no change in the signal and is the reference. When the gain is 0, it is known as unity gain/loss. Typically we would need a microphone that requires a 40 to 60 dB boost in order to order properly.

Describe the concept of "Gain Staging". (2 things we try to avoid & 1 thing to get the output signal to)

We are trying to avoid:

1. Distortion from overloading the signal

2. Too weak of a signal to avoid the noise floor (any voltage drops) We are trying to achieve: 1.a signal level that is high enough going into the next piece of equipment to be at the nominal operation level.

Compare dBV, dBu, and VU.

1. dBV is a scale with a reference of 0 dBV = 1 volt, regardless of impedance.

2. Voltage can use a second decibel scale: dBu. 1 dBV = 2.218 dBu. 0 dBu is dB relative to 0.775 volts.

3. VU is a measure of signal strength compared to nominal level, accounting for headroom. 0 VU is typically +4 dBu, but can change depending on system specifications. The input/output ratings are: -10 dBV = consumer grade +4 dBu = professional grade

Describe the design of a 3-pin XLR cable (why does it have 3 pins, what would each pin carry?) loop from occurring.

Why it is preferred for professional audio applications? What does this mean?

Because is is a common balanced audio connector. Meaning that the cable keeps the low strength signal of a microphone clean and a higher quality output. Advantages are clean audio transfer across long cable lengths and protecting mics and people from electrical damage.

What amount of hertz does a ground loop create?

60 Hz hum

Define sample rate

The time interval that samples are taken, or how many times per second we want to measure the amplitude level of a sound.

Define bit resolution

The amount of values, grows exponentially, as more bits are added to each sample.

What are the 3 quantization errors?

1. Clipping

2. Aliasing

3. Randomize Quantization Error

Define Clipping

Where the audio distorts because the value is rounded down to the highest possible value. A way to bypass this is by avoiding going above 0 dBFS.

Define Aliasing

When a sample rate is too low since the computer can't analyze data out of range and fails to satisfy the Nyquist Theory.

What is the Nyquist Theory?reproduced.

You would need at least a sampling rate of twice the highest frequency of that sound

Define the Random Quantization Error

When the signals keep continuously changing. In order to fix this, one could use dithering

Define dithering

Adding a noise to the signal in order to reduce the overall signal to a ratio and help eliminate distortion

What are the common formats for lossy audio?

1. mp3

2. OGG 3.AAC

Define lossless (uncompressed) audio

Where the PCM data is encoded based on the sample rate and bit depth and nothing else.

What are the common formats for lossless (compressed) audio?

WAV and AIFF (Audio Interchange File Format).

Define lossy (compressed) audio. What does it provide?

Dictates an amount of data that can be stored per second of audio - a bitrate.
It provides a way to store the necessary audio data with the compromise of some reduction in quality.

How does lossless compression differ from lossy compression?

Lossless Compression reduces redundancy in data instead of removing data itself(so that it doesn't have to repeat it and take up space) While Lossy Compression is used to permanently remove data by compressing sound data in a way that discards some information (meaning that it is not restored to its original form after decompression)

What are two benefits of using digital transmission? / Digital transmission allows data to be an EXACT COPY of the original and also lessens interference

1. the ability to send audio over long distances without much interference

2. the ability to transfer PCM audio without any signal loss or degradation between devices.

What is a downside of digital transmission?

digital transmission requires precise time synchronization between the clocks.

How does an ADC ensure proper timing of samples when converting analog to digital?

An ADC uses an internal clock to know at what interval to take a sample. The accuracy of this clock is known as jitter - the less jitter, the more accurate the sampling will be.

How does an ADC ensure proper timing of samples when two devices are connected together?

They use clocking. One of the two devices will be the master, sending the clock signal to the other in a one-way connection.

How does an ADC ensure proper timing of samples when more than two devices are connected together?

They use a Word Clock; one singular master clock that synchronizes all devices

What is a dynamic mic in reverse?

A speaker

Phantom Power

48 volts

Balanced Audio

Ground Loop; stops you from being shocked. Outputs 2 signals; positive signal & negative signal. Flips the negative signal, which increases the amplitude from the signal, and adds it to the positive. Produces noise free audio.

Why do we use Balanced Audio?

Common balanced audio connectors? (2)

1. XLR Cables

2. TRS (tip, ring, sleeve) Cables

What is Unbalanced Audio?

Connectors only supply one signal line and one ground line

Why would we use Unbalanced Audio?

1. Produces a stronger signal

2. Shorter cable runs so less chance of interference

Preamplifiers

A series of transistors that amplify voltage of the input signal without altering the current.

0 dB means what on the relative decibel scale?

no change

Define Gain

a measure of the ability

0 dBV is equal to

1 volt

What do we need in order to recreate audio?

Frequency and Amplitude

Pulse Code Modulation (PCM)

taking samples “snapshots” of audio at specific
intervals and interpreting the values into audio.

0 dBu is equal to

0.775 volts

1 dBV is equal to

2.218 dBU

Low sample rate causes what?

Aliasing. This could lead to silent audio or drop in pitch.

How many decibel scales have we learned about?

1. Relative (dB)

2. dBu

3. dBv

4. dBFS

Decibels Full Scale (dBFS)

0 dB = the max value that can be stored in a digital system using discrete values.

What do peak meters show?

An accurate reading of dBFS value (voltage) in that instant.

Volume Meters (VU meters)

a measure of a signal's strength to nominal level with accounting for headroom