BENEFITS OF THE USB-X4 AND THE PLINK INTERFACES
Any USB interface requires a processor for reception and transmission. The standard also requires a very
specific clock frequency for its basic transmission and, unfortunately, that clock is not any integer multiple of
any audio sample rate. This means that some degree of "frequency beating" can be expected between the
USB clock and the audio sample rate if the USB receiver circuitry is in the same chassis as the digital audio
processor (DAC, player etc.). This can be an audible effect if the product is a DAC.
All our products have an internal USB interface for direct connection to a music server and we designed all
circuits to minimize this interfering beating effect. Ideally, however, one would want to move the USB interface
as far away from the DAC as possible, which would fundamentally avoid this effect completely before it even
happens. While our products with internal USB interface do a good job in compensating for this effect, a
physically external USB interface could provide an extra level of separation that otherwise could not be
possible.
This is where the USB-X4 interface comes in:
Physical separation: It is a USB receiver in an external and separate small chassis that can be placed far
away from the DAC.
Galvanic separation: It then interfaces with the DAC via a very high quality fiber optic cable (PLINK) that
implements a protocol that is synchronous to the audio sample rate (no frequency beating). Furthermore,
since PLINK is a fiber optic interface there is no galvanic connection between your server and DAC. This is an
additional separation that prevents any electrical noise from reaching the sensitive DAC.
Jitter prevention through reclocking: The USB-X4 sports the same reclocking / buffering algorithm
(PDFAS) as all our other products (DAC, transport, player) and therefore provides a second level of filtering
and jitter removal in addition to the connected DAC.
The overall performance improvement can be quite dramatic when compared to a DAC with an internal
USB interface. The sound stage becomes even more alive or vibrant, frequencies are more revealing and
musicality is even more natural.
A quick explanation of the PLINK Interface: PLINK is a high quality fiber optic link used on most Playback
Designs equipment and natively supports all formats of PCM and DSD. Because its media is fiber optic it
separates the sensitive circuitry in your Playback Designs DAC from the generally "noisy" digital sources with
high clock jitter. This separation can result in a dramatic sonic improvement when compared to a direct
connection with the DAC via for instance USB.
The first version of the PLINK interface was launched more than 15 years ago and supported DSD up to
5.6MHz. This version is called "Classic" and is implemented in the 5-series products and IPS-3 (that have not
been upgraded yet). As technology never sits still DSD has been expanded to 11.2MHz several years ago.
Accordingly we also expanded the PLINK format and called it "Sonoma" reminiscent of its origin in the
professional recording tool for DSD (Sonoma workstation) that was developed by the founder of Playback
Designs during the development of the SACD and DSD formats.
PLINK does not use the same media as TosLink, but it is based on a much higher quality and lower jitter
media that is used for very high bandwidth communication links where receivers require an extremely low
jitter signal for reliable decoding. For PLINK we use a much lower bandwidth protocol than the specified limit
of the media to further increase robustness against jitter.
Compatibility: the PLINK interface implemented in the USB-X4 is compatible with the following lines of
Playback Designs products: Sonoma, Edelweiss and Dream series. It is not compatible with the earlier 5-
series products.
