Video, Sound and Multimedia
Video, Sound and Multimedia |
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SOUND
Built-in sound circuitry is routine in today’s PCs. It is vastly improved compared to state-of-the-art computer sound cards of ten years ago. When your PC has a sound card (be it a dedicated expansion card or just circuitry on the motherboard) it can do much more than merely beep through a PC speaker. The sound card plays wave sounds (the recorded sounds you hear when you turn on the computer, run certain programs or when you play a computer game). Most sound cards also play music. Included with the basic audio circuitry is a complete musical synthesizer. You can use this synthesizer to play MIDI files, which produce near-realistic music over the PC's speakers. Sound cards also amplify and play music from your computer's CD-ROM drive. You need a sound card to hear music from a CD if you want to avoid having to plug headphones into the CD player’s headphone jack to do so. With a microphone (and the software that you already have on operating systems such as Windows XP), you can also use the PC's sound card to record your own voice. These recording clips are also saved as .wav files.
The presence of sound connectors (in the form of three tiny jacks) on the rear of your PC confirms that a sound card is installed. The jacks will be labeled Mic, Line In, Line Out, or Speakers and they accept tiny 1/8-inch audio plugs. If your PC has these jacks, it can produce sound. If you have a sound-equipped computer but still can't hear sound, then some troubleshooting needs to be done.
Audio playback on Windows
Several Audio playback programs are selected on your Windows operating system by selecting Start/Programs, then "Accessories" and then "Entertainment". To optimize playback you must have a sound card and speakers installed on your computer.
Windows provides CD player software for playing back CDs.
You can also use Sound Recorder to play back sound files as well as recording and editing sound.
The Windows media player is capable of playing sound files, including .MP3, .WAV and MIDI sequencer files - as well as other kinds of items stored on disk such as Microsoft Multimedia active movie player files, including MPG and AVI files and video for Windows files. Windows XP recognizes the file formats and plays any of them. Of course, you may install other media players that can be a vehicle for sound on your computer (see shortly after most popular plug-ins below). You can also download a sound - dedicated player for CDs and Internet radio, such as Spinner Plus ( http://www.spinner.com/ ).
Connections – for audio input and output
There are jacks on the back of the desktop computer for (from top to bottom) output,
input and microphone:
The out and in jacks are: Line out jacks for external speakers and headphones and
speaker. Your Walkman headphones plug easily into this port. Another use would be to
record MP3s onto a cassette tape.
Line in jacks - use these ports to plug in to record your own voice (using a microphone) or to record other sounds. A standard audio-in port allows you to do a number of things, such as plugging in your turntable and recording your LP’s onto CD. Note the microphone audio input plug:
Laptops’ speakers are usually internal. They may also have lineout for headphones
and speakers and line-in for microphones.
How to set and check sound levels for output and input
When speakers are connected properly, you can easily adjust their audio properties. It is a good idea to play a CD first before adjusting sound properties.
Adjusting audio:
You will likely have a speaker icon on your lower right hand corner of your monitor screen. If not, you can place one there by selecting “Sounds and Audio Devices” from your Windows XP Control Panel and checking "Place volume icon in the taskbar" on the volume tab of the dialog box.
Also called "sound boards" or "audio adapters", these are personal computer expansion boards that record and play back sound, providing inputs from a microphone, or other sound source, and outputs to speakers, or an external amplifier. The de facto standard for sound card compatibility in PCs is Creative Labs' Sound Blaster. Creative labs helped give PCs a sound with its Sound Blaster audio card. Since then progressive generations of SoundBlaster and competing boards have helped to bring the entire range of digital audio recording, editing, and playback functions to the PC. Today, nearly all sound cards are Sound Blaster-compatible, whether or not they share the Sound Blaster brand name. Some high-end sound cards may not be compatible, but they are used mostly with custom sound engineering software. If you wish to see comments on sound cards related to using your computer with a voice recognition software program please see my article "Voice Dictation – Digital Systems" elsewhere in this Syllabus.
Sound cards handle several types of sound. The most common digital audio files that your system plays back is the wave audio (or the Windows .WAV files). Another audio file type, MIDI audio (.MID) has seen much activity in the past few years as an effective way to play back musical scores.
The first IBM PCs were actually capable of playing musical notes, after a fashion, without a dedicated soundboard. This was done by sending electrical impulses (corresponding to frequency and amplitude of the desired sound) over their crude speakers. What sound boards did was to introduce the first tools needed in the evolution toward handling sophisticated sound transactions. Digital to analog converters transform digital signals into analog waves for the speakers to broadcast. In the other direction, analog to digital converters, take incoming sounds from a microphone or line input and convert them into digital ones and zeros for storage on disk.
Most soundboards consist of the following components:
Today virtually all soundboards can record and playback 44.1 KHz, sixteen-bit wave audio.
Some computer systems might not have a dedicated soundboard, but a tiny chip on the motherboard that serves the same function - turning digital files into analog electrical impulses that your speaker can transform into sound. Most modern personal computers, however, do have a dedicated sound card – which is much more to your advantage in dealing with sound input and output.
To offer the most realism in playing back music, Wavetable types of MIDI cards, capable of playing multiple instrument sounds at one time (critical for orchestral sound), have been devised. This multi-instrument capability is described in terms of the number of simultaneous instrumental voices that can be played. The standard instrument library known as General MIDI provides 128 standard instruments. General MIDI-compliant sound cards work within any MIDI file, producing the score using the proper instruments. Virtually all PC sound cards conform to the General MIDI standard although some might offer extended sounds and capabilities.
When buying a sound card there are several different features to check out.
Your sound card should have a high signal-to-noise ratio. The signal-to-noise ratio will help determine how "clean" a sound you can expect from a card. Background noise, the audible hissing that lessens the sound quality produced, results with a lower signal-to-noise ratio. The higher the signal-to-noise ratio, the less hissing. Another advantage of a high signal-to-noise ratio is that when you record, the sound will be clearer. In addition, voice recognition and dictation programs will work better. Most sound cards have a signal-to-noise ratio between 85 and 90 decibels (dB). Some go to 95 dB or higher.
Check out also what Application Program Interfaces (APIs) a sound card has. An API is
an extension for a peripheral that enhances it in some way. Any sound card you find on the
market should already support two APIs from Microsoft, called DirectSound and DirectSound
3D - these are the standard for sound cards. "A3D" from Aureal Technologies can
create an impressive audio 3D effect that is popular with computer gamers. Many sound
cards have a built-in Aureal digital signal processor. Environmental Audio eXtension (EAX)
from Creative Labs creates a more realistic sound and enhances sound by applying effects
to it, such as reverb, rather than creating a positional three-dimensional audio effect as
A3D does. However, A3D tends to create a slightly better 3-D illusion.
One thing you will definitely notice is the number of voices (or sounds) a sound card can
play. The number of voices a card can play at once is called its polyphony. Most sound
cards divide the voices into two categories: hardware voices and software voices. A sound
card will normally play back either 32 or 64 voices at one time through hardware. That is,
the sound card’s digital signal processor plays back the voices so your CPU does not
have to. If your sound card plays back more voices than the sound card can process (for
example, 65 or more), the software voices kick in. You will be able to hear more sounds at
once, but your CPU will have to work to help the sound card process some of the
information. Pay attention to the number of hardware voices. The more voices the sound
card can play through hardware, the better.
Most sound cards come with additional software. If it is something that interests you, see
if the sound card includes MP3 software. Real audiophiles will also want to make sure
their sound card supports four speakers that can create a more realistic 3-D audio
experience. The majority of new sound cards provide four-speaker support.
Digital audio files contain actual sound waves that have been converted into digital form. Without compression, they take up considerable storage space.
Compression is always a trade-off between fidelity and compactness. How much a file can be compressed without noticeably affecting quality depends on how well the compression is done. Most sounds produce a complex set of sound waves and, as mentioned, a digital file retaining 100% of that information can be quite large. However, those sound waves contain a great many nuances that the human ear cannot detect. The information carrying many of those nuances can be removed with no discernable difference to the human listener. The same is true of graphic and video files. The quest to develop new formats is largely one to develop better compression techniques.
The WAV, AIFF, and AU file formats are the non-streaming audio files you are most likely to run across, in addition to MP3 (which is sometimes used for streaming). The native digital audio format for Windows is the wave file (.WAV extension). The Mac uses AIFF, and Sun's AU format is used on the Internet. The most common streaming audio formats are RealAudio, Windows Media, and QuickTime (see "multimedia" on the next page).
The WAV, AIFF, and AU file formats are very similar. Although they were created for use on different systems (WAV for Windows, AAIF for Macs, and AU for UNIX) any audio-playing software you’re likely to find today will play all three. Windows Media Player shipping with Windows XP will play these files. These formats capture the whole sound wave, with very little or no compression, so, as noted above, file sizes can be very large. They are now commonly used for very short sounds, such as the beeps and other notification sounds built into computer software.
The most common sound type, WAV audio, is essentially a digital reproduction of real world sounds. The waveform character of audio is where the Windows audio format, called the "wave file", gets its name. The frequency and amplitude of analog sound (which is essentially vibrations in the air - or some other medium) is represented as a series of digital ones and zeros. The digital-to-analog converter recognizes and converts these bits into familiar sounds (such as musical instruments and people’s voices).
Your PC slices the total curve into lots of small portions - over 40,000 separate slices for each second of audio – in order to represent an analog waveform. Each slice is then given a digital value corresponding to its audio character, up to sixteen bits per slice.
Just a single minute of audio stored on your PC might need more than ten MB of storage space. A ten minute uncompressed wave file will take up 100 MB.
The highest range of audio fidelity is 44.1 KHz, sixteen bit audio, corresponding to the fidelity of audio CDs and the limits of human hearing. Today virtually all sound boards can record and playback 44.1 KHz, sixteen-bit wave audio. Using a lower sampling rate loses much of the analog data that is contained in the curve of the audio waveform.
Compressed audio does not have the quality of CD sound on an expensive high-fidelity system. However, tests at PCWorld (November 2001) showed that most people are satisfied with music compressed in MP3, WMA, Real-Audio or Dolby AAC format if the music files are encoded at high enough sampling rates.
MP3 is the acronym for MPEG-1, Layer III, the latest popular format from the Motion Picture Experts Group. It uses a mathematical formula to interpret sound waves, much as a human ear would, and to discard unnecessary information. As a result, for example, it can reduce music files to about one-twelfth their original size and retain quality close to that of a CD.MP3 actually supports multiple compression ratios. Less compression of course results in better sound, but larger files. The compressibility has made MP3 the preferred format for downloadable music on the Internet. The Internet is full of sites where you can download legal MP3 files of artists promoting their music. However, some individuals have made unauthorized MP3 files of favorite songs and put them on their Web sites without express permission from the artist or recording label; this is in violation of copyright laws. Information on various MP3 players can be found at http://www.mp3.com
The Musical Instrument Digital Interface (MIDI) is a music format. MIDI files (.MID extension) differ from digital audio, because they contain a coded representation of the musical notes of the instrument; for example, middle C on the piano. Thus, unlike other audio formats, MIDI does not contain digitized versions of the sound waves and, as a result, these MIDI files are much smaller than digital audio files. A minute of MIDI music requires just 10 KB of disk space. It is more like sheet music for computers, telling which instrument (or computerized imitation of an instrument) to play, which notes it should play, and when. MIDI was created to allow electronic instruments and computers to communicate with each other. MIDI is good only for playing and creating musical scores. To reproduce voices and animal sounds or most other sounds digitally you need to digitize sound into a wave audio file.
MIDI is a perfect fit for the PC. Not only does it establish specifications sparing everyone the usual standards battle but it also solves many of the thorniest problems with PC-based wave audio. Not only are MIDI files very small but they are also easy to edit, so that users can change instruments, invent new ones, alter a composition and one can also change the relative amplitude and range of instruments using software tools.
MIDI files require a MIDI synthesizer on the sound card although they take up
considerably less space than digital audio files. MPC requires MIDI on the board.
There are two kinds of MIDI sound reproduction methods used in sound cards. FM synthesis
simulates musical notes – but it is an acoustically poor approach (although
inexpensive). Wavetable MIDI synthesis became prevalent when the cost of silicon memory
dropped. Wavetable MIDI (or waveform synthesis) actually holds digitized samples of the
notes (using waveform representations of sounds from actual recording of musical
instruments), producing richer sound. Sound samples of French horns, oboes, violins and
other instruments are accessed from memory and played during MIDI playback. Although the
results obtained from the digital samples used in this method are not perfect, they are
much better than those produced by FM synthesis. Another MIDI feature is the number of
voices, or notes that can be played back simultaneously. High-quality sound cards can have
up to 64 MIDI voices - the new SoundBlaster AWE 64, for example, can output 64 separate
instrumental sounds at once - more than enough for even the most demanding scores.
Today most multimedia PC’s are capable of handling CD-quality digital audio playback and recording, as well as playing back realistic-sounding scores from MIDI files. For best results, though, you will want multichannel audio (to play several independent sounds simultaneously) and polyphonic MIDI (to play MIDI scores that incorporate dozens of instrument sounds). A good baseline for most boards is 20 or 24 note polyphony.
Sound files – making adjustments and selecting a Player on your computer
Your computer may not be properly set up to open your Sound files as you would like to have that done. Furthermore, your computer may not be correctly set to identify certain audio files with a recognizable sound icon (such could be sent to you by e-mail but you may not know what type the file is). To make the necessary adjustments, i.e. to identify and label audio files with a recognizable sound icon or to open your sound files as you would like, do the following:
Creation of one’s own audio files
To create audio files you will make use of the sound card in your computer and a way to input sound signals, such as a microphone or a line out from a stereo. You can obtain sound by inputting from your computer’s CD-ROM player. Or you can record from your stereo or an external CD player - but you use your sound card’s line-in jack, not the microphone jack. Then you will need the appropriate software. The Sound Recorder that comes with Windows XP will let you make .WAV files.
The sound recorder application records your own voice. The sound recorder works just like a tape recorder that enables you to add special effects and even to cut and insert sections of sounds within one another. You can start using the sound recorder on Windows XP by clicking Start/Programs and traveling to the "Accessories" menu. Click on the "Entertainment" menu. Select the Sound Recorder menu item. Windows XP opens the Sound Recorder window. Then, with your activated microphone in place, dictate a phrase.
You will note (while recording the sentence) that Sound Recorder displays the digital wavelength of your voice in the center window. If you want to hear yourself played back - click the rewind button to reset the sound file pointer back to the beginning and then you click the "play" button.
After you create and save sounds, you can embed those sounds in a number of Windows applications including a PowerPoint presentation. In PowerPoint, first you must display the slide on which you want the sound to play. Select the "insert" menu, point to "movies and sounds", and click the desired option: sound from gallery, sound from file, play CD audio track, or record sound. You can also save sounds you have created in the Windows Media folder so that you can add these sounds to the Windows 98 repertoire of possible sound events.
Several freeware and shareware programs will let you record MP3 files.
Copyright © 2003 American Society of Neuroradiology, www.asnr.org