Let’s Talk Music

Audio data is defined by certain parameters, which determine

its quality and format. The major ones are: the sampling rate, number of bits

per sample, and the total number of channels. However, before we take a look at

these, let’s first understand what they’re all about.

Digital audio files are created by taking an analog audio

stream and sampling it at frequent intervals. Sampling rates are specified in

kHz and are measured per channel. So audio data recorded in stereo at 16,000

samples/sec is actually 32,000 samples/sec, since stereo recording involves dual

channels. A higher sampling rate means more number of samples captured per

second, and hence better quality sound. For normal listening, the playback of

recorded sound at a slightly different rate doesn’t show significant

difference in hearing, but for professional musicians who do real-time editing

of audio, even slight differences matter.

The number of bits per sample defines the size of the sampled

data packets. This can be either 8 or 16 bits. Coming to channels, the number of

channels can be equated to the number of paths over which the complete sound is

split. This can either be on the basis of instruments or frequencies. In

professional music recordings, the sound for different instruments is recorded

on to different paths or tracks. This makes them easier to edit. For playback,

the hardware required to handle, say 16 channels, will turn out to be very

expensive. So stereo sound or a maximum of 5+1 channel Dolby surround is enough

for homes. Some movie theatres, however, do have a setup for giving you true

16-channel surround sound.

Making waves

The WAV or ‘wave’ format can be considered as the basic

uncompressed form of audio. Almost all primary recordings of audio or music are

done in WAV format. Since it’s uncompressed, all data remains intact, making

it easy to edit. A WAV file consists of uncompressed 8 or 16-bit sound samples

with a header preface and specifications on how the audio data is formatted in

the file. The sample rates used are typically 11,025 sample/sec for telephone

quality, 22,050 sample/sec for radio quality or 44,100 sample/sec for CD

quality. As for the number of channels, hold your breath, it’s possible to

encode up to 65,536 channels. Most other audio formats use some compression

algorithm or the other, which reduces their size making them unsuitable for

editing.

MIDI

Moving on from WAV, another old favorite in audio is the MIDI

format. MIDI stands for Musical Instrument Digital Interface. It’s basically a

standard for storing sounds from musical instruments like synthesizers and

keyboards. This format doesn’t have any actual sound data in it. Typically, an

MIDI file has instructions that include the note’s pitch, length and volume.

Plus, there are a few other parameters like envelopes, rise, attack and delay

for sound that can also be included in MIDI instructions.

These instructions then direct the digital-to-analog

converter in your sound card to equate them to actual sound samples from the

sound bank for the particular sound card. So, though not always, there’s a

possibility of hearing the same MIDI files differently with two different sound

cards. For professional musicians, this music format is a must as it’s easy to

edit and has lower levels of noise. Most good quality synthesizers in the market

have a MIDI interface that can be connected to PCs and used to create scores.

Software is also available that can convert MIDI sample to written music notes.

So you can simply print these notes and use them for your music class.

MP3

The audio format that’s making waves across geographical

boundaries–MP3–is perhaps the most popular and prevalent of music formats.

MP3 stands for MPEG-1 Layer 3. It’s a digital audio compression algorithm,

which gives you a maximum compression factor of about twelve while still

retaining superb sound quality. Due to this, it takes lesser hard disk real

estate, unlike other audio formats.

MP3 encoding is able to achieve effective compressions as it

works mostly on the range of frequencies perceivable to the human ear. It chucks

out all non-audible frequencies and keeps others for high compression. Ever

since International Organization for Standardization (ISO) formalized this

standard, a number of other high-compression formats have followed. WMA (Windows

Media Audio) is one such venture from Microsoft that’s pitted against the MP3

format. As an inherent part of Windows Me from Microsoft, WMA boasts of better

compressions. People worldwide seem to differ in opinions, some in its favor,

others against it.

AIFF format

AIFF (Audio Interchange File Format) was developed by Apple

Computers, and is the standard audio format on the Macintosh. It’s parallel to

the uncompressed WAV format on the PC, and is therefore meant for easy editing

of audio on the Mac. The AIFF format encodes audio data in 8-bit mono or stereo

waveforms. You can’t compress the data in AIFF, but another version of the

same called the AIFF-C let’s you compress data by a factor of around six.

Apple developed this for recording and storing high-quality sampled audio and

musical instrument information. Apart from the Mac, Silicon Graphics (SGI)

platform and several other professional audio packages use AIFF format for

playing with the sound.

RealAudio

When it comes to streaming audio, Real Audio is the first

thing that comes to mind. It’s a proprietary format of RealNetworks and is

widely used on the Web. The format can be used over the Web or a company

intranet. One advantage of RA is that its content can be customized depending

upon the transmission bandwidth available.

Hardware audio storage

When we talk of music for homes, we have audiotapes and audio CDs as the

storage media. In an audiocassette, data can be stored on the magnetic tape in

primarily two tracks (for A and B sides) and two channels (stereo). The inherent

disadvantage here is that data is accessible only sequentially as the tape

passes under the magnetic head. On the other hand, data on an audio CD is stored

in the form of crests and troughs via burning through a laser beam and accessed

in a similar manner (remember old gramophones). The file format on an audio CD

is raw WAV (CDA). Here, the advantage is that you can quickly jump from one

track to another, so there’s no waiting time.