Empirical Audio Pace-Car USB User manual

Empirical Audio Pace-Car USB User manual
Pace-Car USB User Manual
Empirical Audio Rev. 1.0
© 2010
Pace-Car USB User Manual
Empirical Audio Rev. 1.0
1. Function/Technology
The Pace-Car USB is a versatile hi-res compatible USB interface combined with a
reclocker that can be used with an array of devices including various WiFi devices and
some CD transports. The object of the Pace-Car USB is to reduce jitter in the digital data
stream of streaming audio. Digital data goes into the Pace-Car USB and digital data
comes out, only with lower jitter. The Pace-Car USB incorporates our best low-jitter
technology and includes an array of technical advantages over other devices on the
market, including:
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Galvanic isolation of all inputs to outputs
Async USB, so expensive USB cable is not necessary
External DC power source, allowing battery power
Separate input and output power regulation
High-quality discrete voltage regulation
Precision impedance-matched high slew-rate S/PDIF output
Optimum clocking for best 24/192 performance
I2S output interface for lowest jitter to Empirical Audio DACs
Modular design to allow for clock, power and USB improvements and upgrades
These technical advantages allow the Pace-Car USB to be a world-class digital source,
leaving even the most expensive CD transports and USB converters in the dust.
The sound of the Pace-Care USB is unlike any other digital source. The clarity and
imaging is unsurpassed, allowing you to “see” into the soundstage more than ever
before. Width and depth are improved significantly. It is a totally immersive experience,
the way that music playback should be. More like analog, only better.
1.1. What is jitter?
Jitter is the number one problem limiting the performance of digital audio. Jitter creates
an unnatural, harsh and sibilant sound that is pervasive in digital audio. Jitter causes
listening fatigue with both CD players and computer audio devices. It’s only in the last
three years that the audio industry has become sensitive to jitter and started actively
addressing this. The sound of jitter is like looking through a window with a film on it.
When jitter is reduced, it is like cleaning the window and finally seeing the scenery
outside with crystal clarity and vividness.
Jitter is the inaccuracy in the timing of the digital data. It is not data errors, it is
inaccuracies in the timing of the presentation of the data to the D/A converter. This is
different than sending digital data to a printer for instance, or even a hard-disk. These
data transfers are not “real-time”. Streaming audio data from a CD transport or a
computer source is real-time because the D/A converter creates a real-time analog signal
from the data each time a new data word is presented. If the timing of the presentation of
each word is inaccurate, this causes frequency modulation distortion. There is nothing
that can be done about the samples in the recording and the clock that was used to make
those samples, but playback jitter can be minimized. This is the role of the Pace-Car
USB.
The Pace-Car USB virtually eliminates the sibilance and harshness due to jitter, making
your digital playback closer to analog. The Pace-Car USB is a truly unique and
remarkable product. Once jitter is minimized, the clarity, image focus and dynamics are
improved significantly. Even bass-tightness improves. Recordings of rain, thunderstorms,
violins, cellos, bongos and timpani are finally lifelike.
1.2. Theory of Operation
The Pace-Car USB is a reclocker, meaning that the timing of the data flow into the device
is retimed using an internal clock. The Pace-Car USB reclocker inserts between your
source device or computer and your DAC. The Pace-Car USB buffers the music data
stream in a memory and then reclocks it out with an ultra-low jitter clock. The data is not
modified an any way, it just passes through. There is a small amount of data that is
always stored in the memory, but it will not cause any audible delay in the music start-up.
The only cable that is critical to performance is the cable between the Pace-Car USB and
your DAC. This should be a high-quality S/PDIF coax, AES/EBU or I2S cable to minimize
jitter.
1.3. Modes of Operation
The Pace-Car USB can be used in a variety of different ways, each achieving identical
sound quality:
1.
2.
3.
4.
USB interface from a PC or Mac computer
Mode 1 – Word-Clock driving a stock external source device
Mode 2 – Master-Clock driving a modded external source device
Mode 3 – Pace-Car USB clocks are tuned to a stock external source device
All sources use the clocks inside the Pace-Car USB and the data-stream passes through
the Pace-Car USB. All modes can be used in the same Pace-Car USB, with some Mode
3 sample-rate limitations. The Pace-Car USB uses two separate clocks to support all
sample-rates. Both standard clocks are present in the stock product. One clock is used
for 44.1, 88.2 and 176.4. A second clock is used for 96 and 192. 48 can be optionally
added, but may slightly affect the quality of 192. Upgrades of one or two Superclocks or
one or two Ultraclocks can replace the standard clocks for even better jitter performance.
1.3.1.
USB:
The USB interface is asynchronous, meaning that it does not rely on the timing of
the clock in the computer. This enables great results with inexpensive USB
cables and computers. A USB 2.0 port on the computer is recommended. On
playback, the Pace-Car USB automatically selects the correct clock for each
sample rate. The USB module is isolated from the Pace-Car USB power and
powered from the USB cable. With USB, you basically connect it and forget it.
The Sample-Rate switch on the back-panel has no effect when in USB mode.
1.3.2.
Mode 1:
For Mode 1, the source device must have a Word-Clock input, such as some
high-end transports like the Marantz SA-11S2, some Firewire devices such as
the Fireface400, PCI cards such as the Lynx AES16 or the Transporter. WordClock is a low frequency clock that matches the sample-rate, such as 44.1 kHz.
A Word-Clock cable is connected between the Pace-Car USB and the source
device. The Word-Clock cable is ordered separately and usually terminates into a
50 ohm BNC male connector. This BNC connects Word-Clock to your source
device. The Word-Clock output can be set for 5V or 3.3V logic levels depending
on the source device. This is done at the time of ordering. The customer also
provides two digital cables, one inexpensive cable for input to the Pace-Car USB
and a high-quality cable for output to the DAC. These cables route the digital
data in and out of the Pace-Car USB.
The Word-Clock output on the Pace-Car USB changes automatically to match
the sample-rate of the incoming data-stream within a few clock cycles. The
source device must also respond fairly quickly to changes in the Word-Clock
frequency. If this change takes 30 seconds or more, it is likely that the Pace-Car
USB will overrrun or underrun its buffer. If devices have this delay problem, the
Pace-Car USB can optionally output a fixed Word-Clock frequency. This is a
custom order.
The switch on the backpanel must be in the correct position to match the samplerate of the incoming data-stream. The two positions are: 44/1/88.2/176 and
96/192. Optionally, the second position can be 48/96/192.
1.3.3.
Mode 2:
For Mode 2, the source device must have a Slave-Clock input. This can be
added to Sonos, Squeezebox, Duet, Tascam US-144, and other devices. The
customer must order a modification to add the Slave-Clock input to their source
device. Once this Slave-Clock input is added, the device will not operate without
the Pace-Car USB attached. A master/slave-clock cable is connected between
the Pace-Car USB and the source device. This must be purchased separately.
The customer must provide an inexpensive data cable from the source device to
Pace-Car USB and a high-quality cable from the Pace-Car USB to the DAC.
These cables route the digital data in and out of the Pace-Car USB.
Very Important
In Mode 2, the Pace-Car USB must be powered-on first and the master/
slave-clock cable connected and then power-on the source device.
The switch on the backpanel must be in the correct position to match the samplerate of the incoming data-stream. The two positions are: 44/1/88.2/176 and
96/192. Optionally, the second position can be 48/96/192.
1.3.4.
Mode 3:
For Mode 3, the Pace-Car 2 is tuned to the source computer or stock device and
tracks the rate of the incoming digital stream. Such devices include: Mac Mini,
Macbook, AirPort Express, iPod, Wadia iTransport and Apple TV. The
customer must ship the source device to Empirical Audio so that we can tune the
Pace-Car USB. This requires one day. No mods are required to the source
device. An adapter Toslink cable is included for most devices. There is an
additional cost for tuning and only Superclock4 can be used. With a tuned
Superclock4, the Pace-Car USB can still be used all other Modes, but may be
limited in Sample-Rate. The only cable that must be high-quality is the one used
from the Pace-Car to the DAC. The customer must provide an inexpensive data
cable from the source device to Pace-Car USB and a high-quality cable from the
Pace-Car USB to the DAC. These cables route the digital data in and out of the
Pace-Car USB.
The switch on the backpanel must be in the correct position to match the samplerate of the incoming data-stream. The two positions are: 44/1/88.2/176 and
96/192. Optionally, the second position can be 48/96/192.
2. Front-Panel:
2.1.1.
Input Select Switch
Input selector for S/PDIF coax in, Toslink in and USB in. This can be changed on
the fly to select various sources.
2.1.2.
Power LED
Illuminated when there is DC power to the Pace-Car USB.
2.1.3.
FIFO Overrun indicator
Illuminated when the internal memory has overflowed. For this to occur, the data
input rate must be higher than the data output rate. Check rear-panel SampleRate switch for correct position in Modes 1,2 and 3. Not illuminated in normal
operation.
2.1.4.
FIFO Empty Indicator
Illuminated when the internal memory is empty. Normally on at power-on with no
data sources, or if the data input rate is lower than data output rate. Check rearpanel Sample-Rate switch for correct position in Modes 1,2 and 3. Not
illuminated in normal operation.
2.1.5.
Sample-Rate Indicators
Only one LED is illuminated at a time. Indicates the Sample-Rate of the
incoming data-stream that is selected by the Input Select Switch.
3. Back-Panel
3.1. 12VDC input
This is the power input for the Pace-Car USB. It powers everything, except the USB
interface, which is powered from the USB cable. The power from this goes directly to
the standard clocks, Superclocks or Ultraclocks, so the quality of this power is critical.
Upgrades here make an immediate difference in jitter. Average power consumption is
up to 500ma, depending on clock options, but much higher transient currents are
possible. The standard AC adapter included with the Pace-Car USB supplies 5.5 Amps
@ 12VDC. The connector is center positive, 2.5mm and protected from reverse voltage.
To power-on the Pace-Car USB, plug in the AC adapter and then connect the DC power
cable to the Pace-Car USB. The included AC adapter grounds the chassis of the PaceCar USB to earth ground. Any other AC supplies used with the Pace-Car USB should
also have the ring or minus of the connector tied to earth ground and AC ground.
3.2. S/PDIF Coax input
The S/PDIF input is for use in Modes 1,2 or 3. It should be connected to the source
device S/PDIF coax output using a 75 ohm digital coax cable. This input supports only
PCM data, not AC3 surround. All sample-rates are supported, but must be selected in
two groups using the Sample-Rate switch on the back-panel. The S/PDIF input is
isolated, so the ground return is not connected to the chassis ground of the Pace-Car
USB. The input is terminated in 75 ohms characteristic impedance.
3.3. Toslink Input
The Toslink input (optical) is for use in Modes 1,2 or 3. It should be connected to the
source device Toslink output. This supports only PCM data, not AC3 surround. All
sample-rates are supported, but must be selected in two groups using the Sample-Rate
switch on the back-panel. The Toslink has a door on it that flips up inside when you
insert the optical cable end. Some cable ends are too large and can damage the door,
so if it is difficult to insert, don’t force it. Instead, use a small knife to trim the ridges on
the cable connector a bit to prevent damage to the door when mating.
3.4. USB input
The USB input connects to the source computer, either a PC or a Mac. The USB cable
can be as long as 5 meters and the quality is not important. The 5V power in the cable
is used to power the USB interface in the Pace-Car USB. The USB port on the
computer should preferably be 2.0 compliant. It is recommended that you disconnect
the USB cable only after stopping music playing on the computer. To prevent application
and system crashes, it is best to close the music player application, such as iTunes or
Foobar BEFORE disconnecting the USB cable. Make sure that you load the USB
driver into the computer before connecting the USB cable for the first time.
3.5. S/PDIF Coax Output
The S/PDIF coax output (optionally AES/EBU output) is the primary output that will
connect to most DACs. The return signal on this connector is tied to earth ground and
chassis ground, so the ground used for the Pace-Car USB AC power adapter should be
the same ground used for the DAC. Same AC circuit and phase also. The output
impedance is 75 ohms if the connector is S/PDIF and 110 ohms if AES/EBU. The cable
that connects from this connector to your DAC should preferably be of highest quality
and match the impedance, 75 ohms for S/PDIF or 110 ohms for AES/EBU. The RCA
jack is made of high-quality direct-gold plated copper with Teflon insulator, so it is better
than most BNC connectors. Optionally, a Canare BNC connector can be supplied here,
which is also excellent quality. The cable attached to this connector should be at least
1.0m in length, but minimize the length beyond that. 1.5m is usually perfect and will
work best with other gear.
3.6. I2S output
I2S is a more direct D/A interface than S/PDIF. It was developed by Philips when Philips
and Sony created the CD format and the S/PDIF interface specification. I2S is a three or
four-signal interface that includes clocks. All four signals are provided at 3.3V logic levels
at the Pace-Car USB output, but 5V logic levels are available optionally. I2S is the
native interface for most D/A chips. Therefore if one can drive I2S directly and avoid S/
PDIF translation, there is the opportunity to reduce jitter even more. Empirical Audio
standard I2S interface uses 4 signals and 4 returns and the RJ-45 connector. It is
compatible with I2S on several other manufacturers DACs, including Stello, Perpetual
Technologies and Northstar, as well as our own Overdrive DAC. Other manufacturers
DACs require an adapter cable to make the connection since they don’t all use RJ-45
and the pinouts are not compatible. Most of the other manufacturers DACs also require
the 5V logic level option. Make sure the I2S connectors are mated at both ends of
the cable before powering-on either the Pace-Car USB or the DAC. Likewise,
power both down before disconnecting the I2S cable.
3.7. Sample-Rate Selector Switch
This two-way toggle switch selects between two groups of sample-rates when the PaceCar USB is used in Modes 1, 2 or 3. It has no effect when the USB input is selected. It
is possible to customize these groups for additional fee, such as combining 44.1/96/192
into one group.
3.8. Word-Clock output
Word-Clock is output on a SMA connector with 5V logic levels and 50 ohms output
impedance. Other configurations are optional, including low-impedance, 75 ohms
impedance or 3.3V logic levels. Provides a clock signal equal in frequency to the
sample-rate of the incoming data-stream to a source device, such as 44.1kHz. Turns off
if there is no incoming signal on the selected input. Consult with Empirical Audio to be
sure you have the right configuration for your source device. This output is used in Mode
1 operation.
3.9. Master Clock Output A
A high-frequency clock output for Mode 2 operation on a SMA connector. This is a freerunning clock at 11.2896MHz, with 5V logic levels and 50 ohms output impedance. This
can be changed optionally by Empirical Audio to 22.5792MHz or 45.1584MHz. A Master
clock cable must be connected from this connector to the source device to operate in
Mode 2.
3.10.Master Clock Output B
A high-frequency clock output for Mode 2 operation on a SMA connector. This is a freerunning clock at 24.576MHz, with 5V logic levels and 50 ohms output impedance. This
can be changed optionally by Empirical Audio to 49.152MHz. A Master clock cable must
be connected from this connector to the source device to operate in Mode 2.
4. Software
Software drivers must be loaded to support the USB interface for both PC and Mac before
connecting the USB cable. For operation on a PC, Kernel Streaming is recommended to
bypass Kmixer on XP machines and WASAPI on Vista and Win7 machines.
4.1. USB Drivers
Drivers are located on the included CDROM disk. Load the appropriate driver for your
machine and OS and execute it on the computer before powering the Pace-Car USB or
connecting the USB cable to the computer for the first time.
4.2. Player Software
For PC, the latest version of Foobar2000 is recommended as a player. Install this first.
For XP, a Kernel Streaming plug-in is included on the CDROM. Copy this plug-in to the
“components” folder under C:\Program Files\Foobar2000. Then start Foobar2000 and
select the File pull-down. Then select Preferences. In the Preferences window, go to
Playback – Output – select HiFace Kernel Streaming.
With XP, the sample-rate will be selected automatically. With Vista and Win7, you must
change the sample-rate manually on the computer in control-panel/sounds and audio
devices/advanced.
For Mac, we recommend iTunes with software add-ons such as Amarra or Pure Vinyl to
improve audio quality. If you use iTunes alone, then select HiFace in Preferences/Audio
and use Utilities/Midi options to select the sample-rate. Using iTunes alone requires you
to manually select the sample-rate each time you change to playback of a different
sample-rate.
5. Specifications
Inputs
1. USB
2. S/PDIF coax
3. Toslink
4. 12VDC AC adapter
Outputs
1. S/PDIF coax or AES/EBU
2. I2S on RJ-45, Empirical Audio standard (3.3V or optional 5V)
3. Word-Clock output
4. Master Clock output for 44.1
5. Master Clock output for 96
Controls
1. Front Panel input select switch for USB, S/PDIF or Toslink
2. Rear-panel select switch for 44.1/88.2/176.4 or 96/192
Jitter specs (cycle to cycle, standard clock):
S/PDIF coax output - <1nsec total P-P jitter, <34psec P-P jitter below 1MHz
Master Clock outputs - <250psec total P-P jitter, <27psec P-P jitter below 1MHz
Compatibility
The Pace-Car 2 is designed to work with all DACs and SS receivers/processors. The I2S output
can be converted to 5V optionally for DACs such as Stello or Northstar.
Sample-rates supported by USB/Modes 1 and 2: 44.1kHz, 88.2kHz, 96kHz, 176.4kHz, 192kHz
Sample-rates supported in Mode 3: 44.1kHz, 88.2kHz, 96kHz
Included
1. Pace-Car USB with 2 standard clocks (except with upgraded clocks)
2. 12VDC AC adapter
3. 5m USB cable
4. CDROM with drivers and other software
5. Toslink cable with Pace-Car 2 tuned to Macbook, Mac Mini, Apple TV or AirPort Express
Options
1. Audiocom Superclock4 (required for tuned applications)
2. Second Audiocom Superclock4
3. Audiocom Ultraclock – not for tuned applications
4. Second Ultraclock
5. BNC or NextGen output connector rather than RCA
6. 5 Volt I2S output for Northstar and other DACs
7. Revelation Labs Cryo-Silver Reference I2S cable
8. Word-Clock cable
9. Master-Clock cable
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