Operation Manual

ABOUT AUDIO ON COMPUTERS
280
General Information
Audio Quality
The general audio quality in a computer based synthesizer system depends on two
things:
D The quality of the software calculating the audio.
In our case, this is the Reason DSP (Digital Signal Processing) code.
• Reason uses 32-bit floating point arithmetic for all internal audio operations which
ensures the highest possible resolution throughout the signal chain.
• The program supports 16, 20, and 24 bit audio output.
• The program supports sampling frequencies from 22kHz to 96kHz.
•A number of digital audio techniques are implemented that reduce the risk of
“aliasing”, background noise, unwanted distortion and “zipper noise”.
There is no technical reason why this program should not sound as good as or better
than dedicated, professional hardware.
D The quality of the hardware playing back the sound.
In a PC this is the audio hardware installed. In the Mac it is the built in audio controller
or any audio hardware you have installed.
Don’t be fooled by the “16 bit, 44.1kHz, CD quality” tags. How good some audio
hardware actually sounds depends on a number of things, its frequency range and fre-
quency response curve, the signal to noise ratio, the distortion under various circum-
stances, etc. Furthermore, some designs are more prone to disturbance from the
other electronics in the computer than others. Such disturbance might add hum or
high pitched noise to the signal.
As you probably understand by now, this is a big subject and there’s no way we can
help you find the right solution in this manual. There are a number of text books and
magazines covering this subject and any music dealer specializing in computers will
happily help you out. The only advice we can give is that if you are serious about
sound, choose your audio hardware carefully!
About Latency
On any personal computer system, there is a delay between the moment you “ask”
the hardware to play a sound and when you actually hear it. This delay is referred to as
the “latency” of the design. This imposes a problem for any system where you want
real time user input to affect the sound.
! See the Optimizing chapter for basic information on adjusting Output
Latency!
Why is there latency?
Any audio application creates its audio in chunks. These chunks are then passed on
to the audio card where they are temporarily stored before being converted into regu-
lar audio signals.
The storage place for these chunks are called “buffers” (an analogy would be a
bucket brigade, where a number of people each have a bucket, and water is poured
from one bucket to another to reach its final destination).
The smaller the buffers and the fewer they are, the more responsive the system will be
(lower latency) However, this will also raise the demands on the computer and its soft-
ware. If the system can’t cope up with moving the data to and from the buffers fast
enough, there will be problems that manifest themselves as glitches in audio play-
back.
To make things worse, audio playback always competes with other activities on your
computer. For example, under Windows, an output latency setting that works perfect
under normal circumstances might be far too low when you try to open files during
playback, switch over to another program while Reason is playing or simply play back
a very demanding song.
What is acceptable?
Normally, hardware synthesizers provide you with a latency of 3 to 7 ms (milliseconds
– thousands of a second), at least if the instrument is targeted towards a “profes-
sional” audience.
On a regular PC, the latency can vary quite a lot. This is an effect of the fact that com-
puters and their operating systems were created for many purposes, not just playing
back audio. For multimedia and games, a latency of a 100ms might be perfectly ac-
ceptable, but for playing a musical instrument it is not!
• PC audio cards with a MME driver (see later in this chapter) might at best give you
a latency of around 160ms.
• The same card with a DirectX driver provides at best around 40ms.
•A card specifically designed for low latency, with an ASIO driver, or the built-in au-
dio controller under Mac OS X can usually give you figures as low as 2-3 ms. This
is just as good as (or better than) dedicated hardware synthesizers!
Reason’s built in sequencer is not affected by latency!
When Reason’s sequencer is playing back a song, the timing between notes is per-
fect! Once playback of a Reason pattern or song is up and running, latency isn’t a
consideration at all. The computer clocks the audio between the steps and does this
with perfect quartz accuracy! The timing is immaculate!