Music Tech Flashcards

Particularly aimed at Comp 4 revision

Explain MIDI messages in 5 points:

• Consists of a status byte and 1-2 data bytes

• Each byte consists of 8 bits

• The farthest left bit is called the MSB (most important bit)

• The farthest right bit is called the LSB (least important bit)

• The status byte always begins with 1 and data bytes always begin with 0

What is the difference between a status byte and a data byte?

• The status byte tells us the type of MIDI message

• The data byte(s) provides more information about the associated parameters

What are 2 specific types of MIDI message and what does each byte represent in each message?

Note messages and controller messages

Note messages:

• Status byte = Note on/Channel

• Data byte 1 = Note number

• Data byte 2 = Velocity value

Controller messages:

• Status byte = Control change/Channel

• Data byte 1 = Controller number

• Data byte 2 = Controller value

Explain how MIDI messages transmit velocity data:

• Velocity data is always transmitted as part of the 2nd data byte

• 7 bits are used to represent velocity (because the 1st bit is used to distinguish status and data bytes)

• Because binary is a base 2 system, the number of possible values is figured out using a 2^x calculation

• Therefore, velocity is found using a 2⁷ calculation

• This equals 128 which means that there are 128 possible values for a notes velocity - 0-127

Other then velocity, what are 3 other MIDI messages?

• Aftertouch

• Pitch bend

• Program changes

Explain how to convert from decimal to binary:

Example: convert 98 to a binary number

Step 1: List the factors of 2⁷ from 128 to 1 (128, 64, 32, 16, 8, 4, 2, 1)

Step 2: Find the first number in the list which is smaller than 98 and label that number as 1 (in this case 68 is the first number which will go into 12

Step 3: Label any number before this as 0 (in this case 128 is labled as 0 because it goes 0 times into 98)

Step 3: Subtract 64 from 98 (which equals 34) and find the next number that is smaller than this number (in this case 32) and label this as 1 (label any numbers in between as 0)

Step 4: Repeat step 3 until the whole number is converted (34-32=2, neither 16, 8, or 4 are smaller than 2, so they are labled as 0, Lastly, 2=2, therefore 2 is labled 1 and 1 is labled 0)

What is AAC Codec?

Advanced Audio Coding

What type of data compression is used for AAC and mp3?

Lossy compression

What are 5 benefits of ACC?

• Better sound quality even at lower bitrates

• Uses less power to play audio files

• Supports a wider range of bitrates

• Can handle up to 48 channels whilst mp3 is limited to 2

• Manages higher audio frequencies more effectively

What are 6 compressed digital audio formats and what do they stand for (in alphabetical order - AAFMOW)?

• AAC (Advanced audio coding)

• ALAC (Apple lossless audio codec)

• FLAC (Free lossless audio codec)

• MP3

• OGG (Ogg vorgbis)

• WMA (Windows media audio)

What are MIDI CC?

MIDI Control Changes Messages

Which MIDI CC messages have a value of 0-127?

MIDI CC messages 0-63 (plus many over 70)

Which MIDI CC messages can either be on or off?

64-69 (≤63 off, ≥64 on)

What MIDI CC messages are undefined?

MIDI CC 3, 14-15, and 20-31 

Give a purpose and description for MIDI CC 0:

Purpose: Bank select

Description: Allows user to switch bank for patch selection. MIDI can access 16,384 patches per MIDI channel

Give a purpose and description for MIDI CC 1:

Purpose: Modulation

Description: Generally controls a vibrato effect (pitch, loudness, brightness). What is modulated is based on a patch.

Give a purpose and description for MIDI CC 2:

Purpose: Breath Controller

Description: Associated with aftertouch messages, originally intended for use with a breath MIDI controller in which blowing harder produced higher MIDI control values, can also be used for modulation

Give a purpose and description for MIDI CC 4:

Purpose: Foot controller

Description:  Often used with aftertouch messages, can send a continuous stream of messages depending on how the pedal is used

Give a purpose and description for MIDI CC 5:

Purpose: Portamento time

Description:  Controls portamento rate between 2 notes played subsequently

Give a purpose and description for MIDI CC 6:

Purpose: Data entry MSB

Description: Controls value for NRPN or RPN parameters

Give a purpose and description for MIDI CC 7:

Purpose: Volume

Description: Controls the volume of the channel

Give a purpose and description for MIDI CC 8:

Purpose: Balance

Description: Controls the left and right balance for stereo patches, 0 = hard left, 64 = centre, 127 = hard right

Give a purpose and description for MIDI CC 10:

Purpose: Pan

Description: Controls the the left and right balance for mono patches, 0 = hard left, 64 = centre, 127 = hard right

Give a purpose and description for MIDI CC 11:

Purpose: Expression

Description: A percentage of volume (see CC 7)

Give a purpose for MIDI CC 32-63:

Purpose: Controller 0-31 LSB

Give a purpose and description for MIDI CC 64:

Purpose: Damper Pedal/sustain pedal

Description: On/off switch that controls sustain (0-63 = On, 64-127 = Off)

Give a purpose and description for MIDI CC 65:

Purpose: Portamento On/Off Switch

Description: On/off (0-63 = On, 64-127 = Off)

What is a patch?

A collection of synthesiser settings that make a specific sound

What is the difference between a pulse wave and a square wave?

A square wave has an equal duty cycle (50% - the on/off times are equal) whereas the duty cycle of a square wave is not necessarily equal

What is pulse width?

The duration of “on time” is the pulse width

What is pulse width modulation?

A technique for getting analogue results through digital means. The pulse width is modulated (or changed) to achieve varying analog values