If you're running a computer in the sound room, you have a great opportunity right in front of you.
Part I - Why digital audio?
Most churches still use the venerable cassette tape for
recording audio. While this works fine for many churches, it has a few
- It's very hard to duplicate cassettes - the equipment is
slow, it's expensive, and the sound quality is marginal at best, short
of professional equipment
- It's hard to share easily - other than a cassette duplicator, copying a cassette is a real-time process
- It's hard to archive - cassettes degrade over time, and they take up quite a bit of space
- Fast-forward and rewind are slow and tedious
Consider digital audio for a moment.
- It never degrades with time
- It can be compactly stored - from 10 hours up to hundreds of hours on a single CD, and thousands of hours on a hard disk
- Duplication is easy with most modern computers
- Non-professional CD duplicators are fairly inexpensive
- Instant access to any part of the recording
Part II - Types of Digital Audio Storage
Digital audio is very flexible. Some examples:
- CD burners are available that act just like a cassette tape
recorder, accepting a line-level audio input (such as from a mixing
board) and producing a ready-to-use CD.
- Most computers now include CD writers, that can produce either audio CDs or data CDs.
- Computer sound cards allow the recording of digital audio, and numerous programs are available for this purpose
- Computer hard drives can store digital files once recorded
- Compact discs can be written in data mode, with the files containing compressed digital audio
- Web sites can offer digital audio for playback or download
Part III - Digital Audio File Formats And Sizes
There are a few basic properties of digital audio data that should be understood.
this refers to how frequently the audio is measured when it is
recorded. The higher the rate, the more accurately high-frequency sound
will be reproduced. The laws of nature dictate that to reproduce a
certain frequency, the sample rate must be at least twice as high.
Since human hearing ranges up to around 22,000 cycles per second in
perfect-hearing individuals, audio engineers long ago selected 44,100
samples per second as the standard for compact disc digital audio. As
computer audio matured, this sample rate was retained as the standard.
Some systems use 48,000 samples per second. If high-frequency sound is
not important, some systems use 22,050 samples per second to reduce
Bit depth: this
refers roughly to how many possible steps exist between the quietest
and loudest sounds. The higher the bit depth, the more accurately the
audio will be reproduced. A binary (computer-based) number is
represented in terms of "bits", essentially a one-or-zero value. One
bit can store a single on/off value. Two bits can store four values (0
and 0, 0 and 1, 1 and 0, or 1 and 1). Three bits can store eight
values, and so forth. The compact disc digital audio group selected 16
bits as the standard. Many computer sound cards now reproduce audio
with higher bit depths, sometimes up to 96 bits. Of course, more bits
mean more data, which means larger digital files.
audio data can be compressed many different ways. Compression ratio is
the ratio of the original versus final file size. There are two basic
types of compression - lossy, and loss-less. "Loss-less" compression
means that when the data is un-compressed, it is returned to exactly as
it started before compression. There is no loss of information. This
form of compression is of course desired for text information, or
software, where changing the information would be disasterous. However,
it is also not very efficient for small file sizes. "Lossy" compression
means that some approximations are made when the data is compressed -
the original information can never be exactly recovered. So some
information is lost permanently.
While lossy compression sounds bad, it is in fact not significant in
some situations. The human brain is very good at some tasks, and one of
these is filling in missing data. Most digital photographs are
compressed with the "JPEG" method, which approximates the information
as closely as possible. Depending on how much the picture is
compressed, it will begin to look worse and worse as it it
uncompressed. The same basic situation exists with digital audio
compression - several lossy methods are available which, depending on
the compression ratio, begin to sound worse than the original, but
which can result in astoundingly small file sizes. Essentially, the
compression software analyzes the sound, determines what parts of it
cannot be heard, and discards those.
Aside from the compact disc digital audio standard, which is specific
to CDs, several common formats of digital audio data files exist, that
are relevant to this discussion. Each one is discussed in terms of its
common Windows file extension.
For reference, CD audio is recorded at 44,100 samples/second, 16 bits,
with stereo (two-channel) audio. DVDs use 24 bits at 96,000 samples per
second, and include both stereo and surround sound information.
- WAV (wave) files: this is the largest format of digital
file, but also the most perfect representation. The data is not
compressed. Several sample rates and bit depths are possible for
smaller file sizes.
- WMA (Windows Media Player audio) files: this compression
method is used by the widely available Windows Media Player, bundled
with every copy of Windows sold today. It uses various compression
methods, both lossless and lossy, depending on how much compression is
requested. It also can use various bit depths and sample rates.
- MP3 files: this very common audio file format is typically
based on lossy compression, and like the Windows Media Player files,
can also use various bit depths, sample rates, and compression ratios.
Other uncommon audio file formats include AIF, AU, and OGG files. Which
file format you use is going to be dependent on a number of factors -
one of which is what sounds best to you.
A WAV file from a CD, at 44,100 samples per second, 16 bits,
uncompressed, will typically take about 650 megabytes per hour.
WMA and MP3 files vary widely in file size, but for CD-quality audio
they typically require about 60 megabytes per hour. However, with
maximum compression, WMA and MP3 files can be as low as 3 megabytes per
hour, although this begins to sound like a scratchy AM radio - perhaps
adequate for archival purposes but not for duplication. Still, consider
that at 3 megabytes per hour, two years' worth of Sunday sermons can be
stored on a single CD-ROM - perfect for archival.
For the purposes of this discussion, let's assume that compressed audio
is your choice - you don't want to fill up your entire hard drive in a
matter of weeks.
Part IV - Digital Audio Programs
The list of available digital audio programs is long and complex. For most Windows users, there are two primary choices - Windows Media Player (which comes with Microsoft Windows) and Musicmatch Jukebox.
Each is quite capable, and offers a complete range of recording
compression ratios and file sizes, and each offers a fairly broad set
of playlist tools.
Part V - What To Do With Digital AudioOkay,
so digital audio is cool. No doubt about that; we all have stacks of
shiny, colorful CDs. But what can YOU do with it? Here are some basic
ideas to get you thinking.
We'll cover these ideas in depth in the next article.
- Record your worship and/or sermon direct to digital. Skip the whole cassette thing.
- Record audio CDs for duplication and distribution.
- Duplicate CDs for less than the cost of cassettes. Save your audiovisual department's money.
- Compress the audio files and archive them. Fit your last two years' worth of sermons on a single CD-ROM.
- Upload the compressed audio to the church web site, so anyone can listen to the sermons without picking up a CD.
- Get an advanced digital audio system, and put together your own church worship CD!
Why Digital Audio?
High quality reproduction
Any modern PC
Decent audio card
Some other pages on setting up for digital audio: