Unit Three -- Audio
A digital media primer for geeks - http://wiki.xiph.org/A_Digital_Media_Primer_For_Geeks_(episode_1)
Section 1 - Audio Storage
Section 2 - Formats
Section 3 - Conversion
Section 4 - Audacity Recording
Section 5 - Cutting
Section 6 - Channels
Section 7 - Filters and Effects
Section 8 - Podcasts
Section 9 - Live Audio
Quiz (Sections 1&2)
1 - Human's experience of sound is caused by what?
a) Particles of noise hitting the ear.
b) Changes in atmospheric pressure passing over the ear.
c) Electro-magnetic changes going into the ear.
d) Digital bits inserted into the ear.
2 - A microphone records ______ and converts it into an electrical (analog) voltage.
a) Particles of noise hitting the microphone.
b) Changes in atmospheric pressure passing over the microphone.
c) Electro-magnetic changes going into the microphone.
d) Digital bits inserted into the microphone.
3 - Speakers take in ______ and use it to produce changes in atmospheric pressure that go out from them.
a) An electrical (analog) voltage.
b) Particles of noise.
d) 42 dB
4 - The highest frequency humans can hear is approximately ______.
5 - Decibles (dB) measure the _______ of a sound.
6 - The pressure waves that determine sound can jump from one pressure to another instantaneously.
7 - There cannot be gaps in the measurement of a sound's pressure (waveform)
8 - The best (most accurate) analog to digital conversions use the most samples per second.
9 - The best (most accurate) analog to digital conversions use the least bits per sample.
10 - You can store an analog audio recording directly to your hard drive, without converting it to digital.
11 - Surround Sound uses four channels: Left, Right, Top, and Bottom.
12 - Uncompressed formats are usually (but not always) lossless.
13 - The most common audio format is:
14 - Which of these formats is capable of recording losslessly?
15 - You have a recording that you would like to record in the lowest
possible bit-rate, while still keeping it at high enough quality so it
doesn't sound bad. Which of these codecs would be the best to use?
16 - Which codec is specified as the standard for embedding audio into a website?
Recording and Playback - Activity
Write your answer to the following questions:
1) Where were you born?
2) What are the names of your parents?
3) What is your favorite movie?
4) What is your favorite song? Who wrote it?
5) What time did you get out of bed this morning?
6) What did you eat at your most recent meal?
7) What do you do in your free time?
Now use a microphone and audacity to record your answers to these
questions (you don't need to record the questions, just the answers you
have written out).
Listen to your answers and make sure that they are all clear and easy
Save the project and export the audio out to a .FLAC file.
Cutting - Activity
Create a new project, import the recording of your responses to the
questions in the previous activity (the .FLAC file). Then import
this recording of the questions. Cut and move the sections of
audio around so that each question is followed by the appropriate
Save the project and export the audio out to a .FLAC file.
Channels - Activity
Follow the same steps as the previous activity (import your responses
from the recording activity, and this recording of the
questions). Once again, cut and move the sections so that each
question is followed by the appropriate response, however, this time,
keep them in seperate channels. Once everything is in order, set
the separate channels to left and right audio, so that the person
asking and the person answering sound like they are in different
Filters and Effects - Activity
For this activity, make a recording of yourself asking the questions
(the same questions from the recording activity). Now that you
have a recording of yourself asking and answering the questions,
combine them into the correct order, as was done in the channels
activity. To differentiate the person asking from the person
answering, apply filters such as Pitch or Tempo (or other more advanced ones, feel free to experiment) to each of the
channels to give them their own unique, but still natural sound.
Podcast Creator - Activity
For this activity we're going to create our own podcast. We're
going to start by creating two sepearte audio recordings, episode one
and episode two. Then, using the example of RSS with enclosures,
we're going to create our own feed. Because it won't be hosted on
a web-site but simply in a folder on the computer, don't put http:// in
front of the path, but instead file://. (TODO: Give the example?)
For the final project, you will, with a partner, create a single
episode of a podcast. This podcast episode will be a discussion between
you and your partner, and should last aproximately five minutes. It
will also require one sound effect (to be added in the middle of the
recording, and two background sounds (one for the beginning and one for
the ending) which will be spoken over to introduce the episode and say
Part 1 - Preperation
With your partner write down a list of topics that you will discuss.
This will be the outline for your show-notes. Each partner should
submit an identical list for this exercise. Find audio clips that
you can use for the sound effect, beginning sound, and ending
sound. Each partner should submit identical attributions for each
of these sounds.
Do not go to Part 2 until the teacher has graded this part.
Part 2 - Recording
You should record yourself discussing the topics from your list with
your partner. Each group member should only record the audio for
themselves. Each group member should submit a .flac file with
their recording on it.
Part 3 - Editing
Here we will create the final sound file. Edit the sound recording from
each person who was speaking together with sound effects. Each
person should do their own, independant editing to create the final
Show notes - the outline from part 1 filled in with details about the conversation)
Show Master - A .flac file that is the audio recording in its final form
Show Distribution - An Ogg/Vorbis compressed audio file, that could be distributed in the podcast feed.
Attribution for the sound effects.
Ardor - A professional Digital Audio Workstation. It is a
non-linear editor, with a ton of important features. Available as
free software. http://ardour.org/
JACK - Connector and flow for audio recording.
Podcast Generator - Program that runs on a server and manages your
podcast feed for you. http://podcastgen.sourceforge.net/
Adobe Soundbooth? Adition?
Apple Garage Band?
Envelope Tool - http://www.youtube.com/watch?v=FYA6LmhAzGE (en but no
Sound - Rapid changes in air pressure that can be detected by the human ear.
Waveform - A graph showing the change in air-pressure (also known as sound intensity) over time.
Microphone - A device that turns changes in air-pressure (sound) into changes in electrical voltage.
Speaker - A device that turns changes in electrical voltage into changes in air-pressure (sound).
Cycle - The change in air pressure from a starting point up to a higher
value, down to a lower value, and then back to the initial value.
One cycle is one sound wave.
Hertz - The number of cycles per second, abbreviated Hz.
Pure Tone - A sound composed solely of identical waves at the same frequency.
Amplitude - The height of each wave, measured from the low point to the high point.
Intensity - The strength of the sound, determined by the wave's amplitude.
Decibel - The scale that is used to measure sound, abbreviated dB.
Analog to Digital Conversion - Changing information from an analog
(electrical voltage) to a digital data, abbreviated A-D, A to D, ADC.
Digital to Analog Conversion - Changing information from digital data
to an analog output (electrical voltage), abbreviated D-A, D to A, DAC.
Sample - Each time an A-D conversion happens, the value of the analog signal is stored and referred to as a single sample.
Quantization - The general name for storing analog signals as digital data.
Pulse Code Modulation (PCM) - The most popular method for storing the analog
signals of audio in the digital form. This gives each pulse (or
sample) a code based on the number of available bits.
Sample Depth - The number of bits used to encode each sample.
Sample Frequency - The number of samples that are taken ever second.
Channel - One microphone's audio recording. Two channels can be
combined for stereo sound, six channels can be combined for surround
Track - A recording of one channel.
Bit Rate - The number of bits per second that are used to store the audio as digital data.
Constant Bit Rate - Every portion of the recording is encoded at the same rate.
Variable Bit Rate - The bit rate of the recording can change throughout
the recording so that parts that are complicated can use more bits and
parts that are simple can use less bits, while maintaining the same
overall bit rate.
Rip - Take the data off of a CD (or DVD) and store it to the hard disk.
Burn - Write data to a CD (or DVD).
Silence - An absence of audio (no pressure waves causing changes).
Shift - A tool in audacity that can be used to move selections forward or backward in time.
Envelope - A tool in audacity that can be applied across an audio track to increase or decrease the intensity for various spots.
Amplify - Increase (or decrease) the intensity of a selection.
Fade - Have a sound gradually come up from silence (fade in) or go down to silence (fade out).
Compress - Make the audio intensity use a smaller range.
Pitch - The tone of the sound.
Tempo - The speed at which the beat of the sound comes.
Podcast - An episodic audio show, that can be automatically downloaded to many listener's computers.
XML - eXtensible Markup Language, a way of representing data as text, using tags for data types.
RSS - Really Simple Syndication, the XML format used for feeds of podcasts, blogs, news streams, etc.
Show Notes - A set of information with items of interest from a podcast episode.
Stream - Audio or video that is coming over the internet that can be
heard immediately after it arrives (as opposed to a download where you
wait for it to complete).
Signal Sampling, Binksternet, http://commons.wikimedia.org/wiki/File:Signal_Sampling.png,
PCM Graph, Ktims, http://commons.wikimedia.org/wiki/File:Pcm.svg,
Clipping Graph, David Batley, http://en.wikipedia.org/wiki/File:Clipping.svg,