DAC1 USB
Instruction Manual Revision D Page 23
Mac OS X Test Results
The system sample rate must be set to match
the sample rate of the files being played, and
the system volume control must be set to
100%.
Like the Windows® XP and 2000 operating
systems, OS X has very poor-quality sample-
rate-conversion. The system sample rate is
manually set and must be set to match the
sample rate of the audio being played. This is
not a problem if the system will always be
used at a single sample rate such as CD’s at
44.1 kHz.
OS X also has a poor quality master volume
control. It will degrade the quality of the
audio if it is not set to 100%. Fortunately it is
bit-transparent when set to 100%.
OS X is capable of bit-transparent audio
playback when the system sample rate is set
to match the audio, and the system volume
control is set to 100%.
Advantages of 24-bit Playback of
16-bit Sources
Why do I need a 24-bit USB audio device to
play 16-bit 44.1 kHz music files?
The reason is that digital volume controls and
digital mixers increase the word-length of the
audio. The longer word-length is a result of
multiplication and addition. These arithmetic
operations produce long word-lengths that
must be squeezed back into a shorter word
length. Word-length reduction adds noise
and/or distortion to the audio. The amount
that is added is determined by the output
word length.
The noise and/or distortion added by word-
length reduction decreases by 6 dB for every
additional bit that can be retained. Reduction
to 16-bits adds 48 dB more noise than
reduction to 24-bits. In general, 16-bit word-
length reduction is very audible; while 24-bit
word-length reduction produces noise levels
that are well below audibility.
Our tests show that 24-bit output devices
deliver a dramatic improvement in sound
quality when playing 16-bit material. Native
USB output devices have had a reputation for
poor sound quality. This is primarily due to
the 16-bit word-length reduction.
Benchmark’s Advanced USB Audio
technology breaks the 16-bit barrier and
delivers pristine digital audio to the D/A
converter. Benchmark’s UltraLock™ system
insures that the D/A converters deliver this
audio to the analog outputs without adding
jitter-induced distortion artifacts.
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