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Audio FAQ ... Questions
General
What is the difference between Real Streaming Audio & MP3 Audio?
What is a .wav file?
How big are audio files?
How do you convert a CD to an MP3?
What is an MP3?
Are MP3's legal?
Why can't I just copy the .cda file from my Audio CD?
Are there any good sound effects libraries available?
How do I edit audio files?
Who can use the UI's Stream Server?
PowerPoint
Should I use sound effects in my PowerPoint presentation?
What type of audio files can PowerPoint play?
Websites
How do I stream audio from my website?
Where can I find sound effects?
Where can I learn more about audio?
Audio FAQ ... Answers
What is the difference between Real Streaming Audio & MP3 Audio?
Real Audio
Real Audio is streaming media—which is to say that it starts
playing very soon after you click on a real audio hyperlink and
continues to play while the rest of the lecture is downloading
in the background. This format requires an Internet connection
each time a student listens to a lecture. An advantage of this
format is that a student may begin listening to the audio
lecture almost immediately without having to wait for the entire
audio file to download to a local computer.
Real Player is required to hear the streaming audio material
available below.
Real Player
Download
MP3 Audio
MP3 is a standard non-streaming audio file format. It must be completely downloaded to a computer before it can be opened and listened to. An advantage of this format is that an audio file may be downloaded ahead of time and thus, does not require an Internet connection during the time a student listens to the lecture. These files may also be transferred to a mobile device (e.g. iPod, MP3 Player) allowing a student to listen to a lecture while away from a computer.
MP3 audio files may be played using many different multimedia packages including Windows Media Player and iTunes. To download an MP3 audio file, right click on the corresponding hyperlink and select Save Target As...
What is a .wav file?
At the most basic level, computers capture sound by taking a stream of analog music and converting it to a digital form using special chips known as ADCs (analog-to-digital converters).
Note To be more exact, you will see ADCs typically referred to as either A/D converters or even just AD converters (without the forward slash). Conversely, there are also digital-to-analog converters—known as either DACs, D/A, or DA converters—as well as converters that handle both (AD/DA converters).
ADCs take a signal from a microphone, audio tape, or some other analog source and convert it to a digital signal that computers can understand and save. Nearly every soundcard available today includes one or more ADC.
As the soundcard reads the audio signal, the ADC passes the digital information to your computer as raw data. This information passes through the sound card driver software, to the operating system and to whatever recording program you are using. This process is called sampling, because the computer is actually taking tiny samples of the audio stream and turning it into a numerical equivalent it can later use to re-create the audio it has captured.
This type of file can be saved as a .wav file - the kind of file you will find on Audio CD's.
Adapted From:MP3 Power! with Winamp
Justin Frankel, Dave Greely and Ben Sawyer
Copyright © 1999 Muska & Lipman Publishing
How big are audio files?
Sampling
"While sound is a continuous stream of
information, a computer needs to take small samplings of sound at
constant intervals in order to record. If you sample the input more
often, you’ll be able to reproduce a more accurate, better sounding
output when the time comes to play it back. The rate at which you
sample (or the sampling rate) is usually measured in Hertz (Hz) or
kHz, which is 1000 Hz. One Hz means once per second. Sixty Hz means
60 times per second (which happens to be the rate at which
fluorescent lights buzz). A 44.1 kHz sampling rate means that the
audio was sampled 44,100 times per second.
The more often the sound is sampled, the more accurate the sample
gets (meaning it sounds more like the original), but you also accrue
more data, and thus a larger file results. Most high-quality,
CD-style samples are collected at a 44.1kHz sample rate. When
sampling at a lower rate for smaller files, most programs offer
22.05kHz (one half) or 11.025kHz (one quarter) rates.
Channels
A Channels count refers to how many different unique audio signals there are in a file. For example, most tapes and all CDs include a stereo signal, which means there are two channels—left and right. AM radio, for instance, is usually a mono signal. Stereo signals tend to require twice as much data as mono signals, since there are two separate signals.
Resolution
While sampling determines how often you capture a segment of sound, it doesn’t determine the precision of the sample. Precision is usually determined by the resolution of the sample, which is measured in bits per sample. Having increased resolution makes sounds have less background noise. For example, 16-bit samples allow sounds with nearly no noticeable noise to be reproduced, while 8-bit sound tends to have a pretty noticeable amount of noise. The only downside to 16-bit samples over 8-bit samples is they take up twice as much information.
One thing to be sure about is that your system is set up properly to provide good quality sampling. Some pieces of audio sampling software don’t automatically default to using the highest quality settings of your sound card.
Note: Many popular consumer level, and some professional level, audio sampling software will typically by default sample at 8 bits during simultaneous recording/playback. Be sure to change to 16-bit samples for adequate sound quality."
Adapted From:MP3 Power! with Winamp
Justin Frankel, Dave Greely and Ben Sawyer
Copyright © 1999 Muska & Lipman Publishing
The Math for 1 minute of CD quality audio
- (60 seconds)x(2 channels)x(16 bits)x(44,100 samples) = 84,672,000 bits
- 84,672,000 bits / 8 bits = 10,584,000 Bytes
- 10,584,000 bytes / 1024 bytes = 10,335 KiloBytes
- 10,335 kilobytes / 1024 kilobytes = 10.1 MegaBytes or 10.1MB
| 44.1 kHz | ||
| stereo | mono | |
| 16 bit | 10.1MB | 5.0MB |
| 8 bit | 5.0MB | 2.5MB |
| 22.05 kHz | ||
| stereo | mono | |
| 16 bit | 5.0MB | 2.5MB |
| 8 bit | 2.5MB | 1.3MB |
| 11.025 KHz | ||
| stereo | mono | |
| 16 bit | 2.5MB | 1.3MB |
| 8 bit | 1.3MB | .6MB |
How do you convert a CD to an MP3?
The process of converting CD files to .mp3 files is sometimes referred to as "ripping" a CD. The process involves placing a CD in your CD-Rom driving and using a piece of ripping software. This extracts the .wav file and in some cases also encodes it to an .mp3 in a single step process. If you don't have any software, try this site, you can also download demo and trial versions. Audiograbber is an easy to use software package. It is about $20 and well worth buying if you plan to rip many CD's.
What is an MP3?
"MP3—short for MPEG Layer 3—allows you to store music or other audio files on a computer disk so that the file size is small, but the quality is near that of a compact disc. Without the compression of MP3, a one-minute CD-quality recording would take up more than 10MB of disk space. MP3 compresses most sound files 10 times or more.
MP3 was created as an extension to the MPEG format, an openly developed standard for compressing and transmitting video and audio content over networks—be it satellite, phone, wireless or even the Internet. The MP3 technology was primarily developed by engineers at the Fraunhofer Institute in Germany. MP3 is an ISO (International Organization for Standardization) standard, which means it is not controlled by any single private organization, but is defined very clearly and cannot change without ISO’s approval. Fraunhofer and Thompson Consumer Electronics, however, do hold certain patents and commercial rights on the MP3 technology."
Adapted From:MP3 Power! with Winamp
Justin Frankel, Dave Greely and Ben Sawyer
Copyright © 1999 Muska & Lipman Publishing
Are MP3's legal?
MP3 is a file format that can be used legally or illegally. This analogy explains it best: Cars are legal but using one to run someone over is illegal. MP3 is legal when used to encode music from your own CDs—if you keep that music to yourself; much like making your own cassette copy of a CD or another tape or record. It is illegal to encode MP3s and trade or sell them to others unless you have the permission of the music’s copyright holder. In other words, if a record company or band makes MP3 files available for download, they are yours for the taking (but not to give or sell to others). However, converting your new Hole CD to MP3 and then offering that as a way for people to get the music without buying the actual CD is illegal."
Adapted From:MP3 Power! with Winamp
Justin Frankel, Dave Greely and Ben Sawyer
Copyright © 1999 Muska & Lipman Publishing
Why can't I just copy the .cda file from my Audio CD?
The .cda file that you see when you place an audio CD into your computer is simply a link to the uncompressed .wav file also stored on the disc. in order to get a copy of that .wav file, you must "rip" the track. See "How do you convert a CD to an MP3?"
Are there any good sound effects libraries available?
Yes. But, you have to pay for them. Here is a great set called BackTraxx from a company called Digital Juice or you can buy a cheap set, but you get what you pay for!
How do I edit audio files?
Our recommendation is Audacity. There are many other programs to choose from at www.SharewareMusicMachine.com.
Who can use the UI's Streaming Server?
The UI Streaming Server is available to UI faculty and Staff for UI related projects.
Should I use sound effects in my PowerPoint presentation?
Typically it is a good idea to make your PowerPoint presentation a supporting element of your already strong and well thought out presentation. Many people make the mistake of assuming a great presentation is one with lots of sounds effects, 3D graphics, flaming logos and funny home-video clips. Entertaining as these may be, they don't always come across as intended. It is recommended to use sound effects if they will enhance your presentation, and make your message stronger.
What type of audio files can PowerPoint play?
PowerPoint 2002 can play almost every file that your computer can play with the exception of RealAudio (.rm) files. These files can be played by creating a hyperlink to the file from the slide. The list below is not exhaustive, but should cover many of the common formats.
- Apple AIFF (.AIF)
- MPEG Layer 3 (.MP3)
- Next/Sun (.AU)
- Windows PCM (.WAV)
How do I stream audio from my website?
The first thing involved in streaming files from your website is to find a place to host the files. The UI has a RealVideo/Audio streaming server, contact a staff member at the CTI for further assistance in setting up a folder on this server. Secondly you need to convert your files into RealAudio files. This can be done by using a product called RealProducer. RealProducer can be download and used in a limited capacity for demonstration, you will find a copy here. Scroll to the bottom of Real's page to find the free download.
Where can I find sound effects?
Try:
www.findsounds.com
www.sounddogs.com
Where can I learn more about audio?
To learn more about digital audio, purchase a copy of "MP3 Power!" or if you are on the University of Idaho campus (Moscow), try accessing it from 24x7 Books.
You might also be interested in the:
Sound Reinforcement Handbook
by Gary Davis & Ralph Jones