JOPLIN
384
k
H
z
/32bit ANALOG-TO-DIGITAL CONVERTER
REVISION P
R
A – SEPTEMBER 2012
Copyright © 2012, M2Tech Srl
26
M2Tech
www.m2tech.biz
8.3.3. Sampling frequency
The
Joplin
can operate at the following sampling frequencies: 44.1kHz, 48kHz, 88.2kHz,
96kHz, 176.4kHz, 192kHz, 352.8kHz and 384kHz. The higher the sampling frequency, the
larger the files produced when recording the data out of the ADC, but also the higher the
sound quality. Thus, the choice of the sampling frequency is a trade-off between disk
usage and quality.
On the other hand, when using the
Joplin
to drive a digital amplifier, a DAC or a streaming
player for real-time playback, the best choice is always the highest sampling frequency
possible.
NOTE: The sampling frequency set by the user via the menu is used when the
Joplin
Joplin
Joplin
Joplin
is not connected to any computer, otherwise the parameter is ignored and the
actual sampling frequency is the one set by the computer audio control panel or by
the recorder program. The value set via the menu is restored as soon as the
computer is disconnected from the
Joplin
Joplin
Joplin
Joplin
or it is shutdown.
NOTE: the highest sampling frequencies available (352.8kHz and 384kHz) are not
settable by the user via the menu. This is because in standalone use the only usable
outputs are the S/PDIF, AES/EBU and Toslink™ ones, which cannot operate at
sampling frequencies higher than 192kHz.
8.3.4. Resolution
The
Joplin
can operate at the following resolutions: 16 bits, 20 bits, 24 bits, 32 bits. As for
the sampling frequency, the higher the resolution, the larger the files produced when
recording from the source but also the higher the sound quality.
The ADC works natively at 32 bits. Thus, when a lower resolution is chosen, it is
necessary to get rid of some bits from each sample acquired by the ADC. This operation
generates distortion in the sound.
For this reason, The three lower resolution settings are available in two flavours: with
dithering and without dithering. The dither is a small random noise which is added to the
sound before reducing the resolution. The dither turns the distortion due to the resolution
cut into white noise, which is far more pleasant to the ear.
When SNR is a main goal and a little distortion can be tolerated, dither should be avoided.
On the other hand, when the best sound is desired at the cost of a little added noise, dither
is mandatory.
It should also be considered that the S/PDIF, AES/EBU and Toslink™ outputs can only
transfer 24 bits per channel. Thus, the “24
D
” value should be chosen to obtain the best
audio performance out of the digital outputs.
