Audio & Midi Protocols 2

Question 1

Header

Answer 1

At the beginning of each frame is a header that identifies the packet. The heads act as synchronizers, setting up points throughout the mp3 file at which playback can begin in the middle of a song. The headers permit fast forwarding and reverse.

Question 2

Tag

Answer 2

contains information about the song, including name, artist, album, length and track number. The mp3 player uses this information for its display while the song is playing.

Question 3

MP3 Data

Answer 3

the rest of the file is audio data, in the form of bits, that has been compressed during the creation of the file

Question 4

Ogg

Answer 4

Hardware manufactures can support Ogg Vorbis in their designs without having to pay license fees. Users can modify the format’s code for their own needs. It also supports up to 255 distinct channels, instead of just 2.

Question 5

Typical Bitrates

Answer 5

8 kbit/s Telephone quality (using speech codecs).
32 kbit/s AM Quality.
96 kbit/s FM Quality.
128 kbit/s -160 kbit/s Was the standard bitrate quality.
192 kbit/s DAB Quality.
224 kbit/s - 320 kbit/s Near CD Quality.

Question 6

Constant Bit Rate

Answer 6

means that each sample of the encoded file must use the same amount of bits.

Question 7

Average Bit Rate

Answer 7

average amount of data transferred per unit of time, usually measured per second

Question 8

Variable Bit Rate

Answer 8

This gives the encoder the freedom to save bits on simple sections of audio that don’t need as many bits and vice versa.

Question 9

Analog Communication

Answer 9

is a type of communication where an analog signal is transferred between two devices through a medium. It can be transmitted through either wired or wireless communication.

Question 10

Single Core / Shielded Cable

Answer 10

The single core is used for the +ve, or ‘hot’, and the shield is used for the -ve, or ‘cold’. This type of cable is used for unbalanced audio signals.

Question 11

One Pair / Shielded Cable

Answer 11

This cale has one core as the +ve, and the other core is -ve. The shield is earthed. This type of cable is used for balanced audio signals.

Question 12

Balanced Audio

Answer 12

works on the principle that two identical signals which are
inverted 180°out of phase will cancel each other out.

Question 13

Unbalanced Audio Cables

Answer 13

uses two lines to transmit the audio signal -a hot line which carries the signal and an earth line. This is common in short cables (where noise is less of a problem) and less professional applications.

Question 14

Balanced Audio Cables

Answer 14

Consist of a hot line, cold line and earth. The audio signal is transmitted on both the hot and cold lines, but the voltage in the cold line is inverted therefore the two signals are 180 degrees out of phase with each other.

Question 15

Digital Communication

Answer 15

Only uses a wired medium for the transfer of data. The digital signal can have multiple discrete values but when they are represented using only two possible values of amplitude they are called a binary signal. The binary signal or data exists in the form of bits whose amplitude is either only “0” or “1”

Question 16

Digital Interconnects

Answer 16

The binary data exists in the form of bytes where each byte is made of 8 individual bits. Therefore, the digital signal can be sent bit by bit in a sequence or we can send the whole byte at a time.

Question 17

Synchronous Communication

Answer 17

occurs between two devices when a clock signal is sent along with the data (either on separate wires, or modulated with the data).

Question 18

Asynchronous Communication

Answer 18

occurs when the sending and receiving devices are not locked directly, but have the same frequency - well suited for applications where messages are generated at irregular intervals.

Question 19

Isochronous Communication

Answer 19

is where a network has a master clock signal to which all devices are synchronized.

Question 20

S/PDIF (Sony/Philips Digital Interface)

Answer 20

In case of S/PDIF, the send rate is the sample rate as well. As this rate is generated by the clock of the sender, any fluctuation in the send rate manifest itself as input jitter at the DAC. S/PDIF is therefore a hybrid signal, the data is digital but the timing is analog.

Question 21

HDMI

Answer 21

the audio clock is derived from the video clock. For high-definition TV, the video clock runs at 74.25 MHz. The audio clock runs at multiples of 48 kHz.

Question 22

MIDI Time Code (MTC)

Answer 22

is time-based only relating to hours, minutes, seconds and frames, not measures or tempo.

Question 23

MIDI Clock

Answer 23

is a measure driven pulse (beat) clock. Carries Play, Stop, Forward, and Backward commands as well as tempo data. Ability to slew to tempo changes.

Question 24

OPEN SOUND CONTROL (OSC)

Answer 24

Typically transmitted over Ethernet. OSC has a binary data section, but a human readable, URL-style address that looks like “/foo/bar”. OSC allows one to transmit multiple data types commonly used on modern computers including 32-bit integers, floating point numbers, strings and more. OSC includes a high-precision timestamp with picosecond-resolution that allows OSC messages to be scheduled, recorded and reproduced with minimal jitter.