happens). In addition to aliasing, sampling too slowly will result in reduced
high frequency reproduction. Your Echo card allows you to sample sound at
up to 96,000 times per second.
Once the waveform has been transformed into digital bits, it must be stored.
When sampling in stereo at 96kHz using a 24-bit word size, the system has
to accommodate 4,608,000 bits per second. In the past, storing this vast
amount of data was problematic. Today, computer-based digital recording
systems record the data directly to the computer’s hard disk. Today’s hard
disks are capable of storing large amounts of data, though the performance
of hard drives can vary substantially. The speed and size of your hard drive
will be a major determining factor in how many tracks of audio you will be
able to simultaneously record and playback.
Decibels
Audio signal levels are generally expressed in units called “decibels” which
are abbreviated as “dB”. This is a “logarithmic” scale where each doubling
of signal level is represented by an increase of 6dB. Therefore a signal of
6dB is twice as big as a 0dB signal and a signal of 12dB is four times as big
as a 0dB signal.
Since digital audio signals are represented by binary data, each bit of audio
information represents 6dB. A 16-bit number can represent a total range of
96dB and a 24-bit number can represent a total range of 144dB (6 times the
number of bits). It’s much easier to say that one signal is 72dB less than
another instead of saying it is 1/4096 the size of the other one. It also more
accurately represents the way we hear sounds, since the smaller signal in the
above example will still be audible and not appear to be only 1/4096 as loud
when we listen to it.
Just as there are different types of degrees used to represent temperature
(Fahrenheit, Celsius, etc), there are different types of decibels used to
represent the level of analog audio signals. The most common are dBu and
dBV decibels. Both of these represent voltage levels and still double for
every increase of 6dB. It is only the reference point, or 0dB level that is
different. A 0dBV signal has a voltage level of 1.0 volts. A 0dBu signal has
a voltage level of .775 volts. Since .775 is approximately 2dB less than 1.0,
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