User Guide and
Technical Information
page 21
SOUND DEVICES, LLC
When connected to the computer, the USBPre is
a highly integrated part of the PC that relies on
the host (computer) to handle data traffic in and
out of its hardware. With late model computers
there is sufficient processing power to handle all
of the tasks of computing along with audio. The
performance of the USBPre with your system is
dependent on three major factors - the hardware
configuration, operating system configuration, and
the audio software configuration. To obtain the
best performance from the USBPre optimization of
each of these factors is recommended.
Assuming that the computer system meets the
minimum requirements outlined in this documenta-
tion there are other areas that can be optimized.
Memory
Sufficient RAM is important for audio applications.
Since a system with insufficient RAM must access
the hard drive as virtual memory, the data flow is
slowed greatly in and out of the processor. 128 MB
of RAM or more is highly recommended for most
audio applications.
Hard Disk
Multi-track audio recording is a hard disk intensive
activity. As an audio production increases its track
count, the demands on the disk drive increase.
In general, higher rpm drives have greater sus-
tained throughput than low speed drives. High
sustained transfer rates are more important than
high burst rates when comparing hard drives for
audio (and video) applications. SCSI drives typi-
cally have higher sustained throughputs than IDE
drives, although newer IDE implementations have
sufficient data rates for audio. Depending on the
computer system, increased hard disk activity can
interfere with (interrupt) the USB bus, resulting in
audio dropouts. In general, disk drives with fast
sustained data rates and large memory caches
perform best for multi-track audio.
Buffer Adjustment
Many audio applications have selections to adjust
playback and record buffer sizes. These adjust-
ments change how much audio data is retained in
RAM. With too small of a buffer, audio hardware
runs out of audio data before it can be read from
the hard drive. Typically, larger buffer sizes improve
stability of audio applications at the expense of
program responsiveness. Refer to you software
documentation for guidance in adjusting buffer
sizes.
Power Management
Power conservation is a significant issue for note-
book computer designers and is becoming more
popular on newer desktop computers. Most com-
puters are shipped from the factory with some
power management applied. Audio applications
and USB audio work best when all power manage-
ment is deactivated. Power management can spin
down hard disks, slow processor and bus speeds,
and shut down displays. Often, when recording
long programs, the computer keyboard and mouse
are not touched. The computer thinks that it is idle
and goes into standby mode. The change in state
can cause audible artifacts when recording and
playing.
Notebook Computers (Windows)
Many notebook computers share IRQ’s between
the display adapter or other devices and the USB
controller. This causes additional traffic on the
USB’s interrupt. To check for this condition, fol-
low Start>Settings>System and select the Device
Manager tab, select Computer and click on
Properties. This reveals the list of system inter-
rupts. If any device (except for “PCI steering”)
shares an IRQ with the USB Host Controller, try
removing any unused hardware devices to free
up IRQs and turn off hardware acceleration to
improve USB audio performance. To turn off hard-
ware acceleration follow
Start>Settings>Control
Panel>Display
, select the Settings tab, click
“Advanced..”, select the Performance tab and slide
the control to the None position.
USB Audio Optimization
audio, or a mix of both. When monitoring analog
input audio, the audio playing in the headphones
is the direct analog signal before any digital con-
version has occurred and before it is sent to the
computer. When monitoring PC audio, the com-
puter controls the digital audio. Note: The Windows
Volume Control (controlled with the “speaker”- icon
in the system tray) and the Mac volume control
adjust the level of the computer audio in the head-
phones and at the PC Audio output.
