Empirical Audio Off-Ramp 4
Low-jitter USB digital audio converter
The Off-Ramp 4 is a fourth-generation product that provides a USB computer interface to your audio system with unprecedented sound quality. The Off-Ramp 4 supports sample-rates of up to 24/192 and uses Asynchronous USB protocol*, which is optimum for reducing jitter. A custom Software Driver is provided and must be loaded for the Mac or PC. This driver has been shown to be more reliable and trouble-free than the native Microsoft driver.
The Off-Ramp 4 allows you to add a high-performance USB interface to your existing non-USB DAC. It can also improve on the existing computer interface on your USB or Firewire DAC. Most DACs with USB or Firewire interfaces will sound better when an Off-Ramp 4 drives their S/PDIF input.
The Off-Ramp 4 is a reference quality 24/192 reclocker that will challenge the very best and most expensive CD transports and music servers. The difference between the Off-Ramp 4 and other manufacturers converters is not subtle. The Off-Ramp 4 delivers clarity, depth, width and imaging that is unsurpassed. The system that won best of show from TAS at the 2010 Rocky Mountain Audio Fest used the Off-Ramp 4.
Our customers tell us that:
“The soundstage is wider with much greater depth. I no longer hear the occasional high frequency harshness with previous computer-based transports. The sound is relaxed, natural and analogue..”
Michael L. 12/2010
Minimizing Jitter
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.
The Off-Ramp 4 virtually eliminates the sibilance and harshness due to jitter, making your digital closer to analog. Once jitter is minimized, the clarity, image focus and dynamics are improved significantly. Recordings of rain, thunderstorms, violins, cellos, bongos and timpani are finally lifelike. The Off-Ramp 4 is so good at reducing jitter that it is used by reviewer Steven Stone of TAS.
Features
Clocks
Two clocks are required in the Off-Ramp 4. These clocks are the oscillators that move the datastream from the Off-Ramp 4 to the DAC. Since the computer clock is not used, except for moving blocks of data into the Off-Ramp 4, these two clocks are the real-time “Master” clocks. The jitter of these is critical. Two clocks are needed to cover all sample-rates because these clocks are free-running without any PLL. Two standard clocks are provided on the standard version. All sample-rates are generated by dividing-down the frequency of these two clocks. Because the sample rate groups are not mathematically related, the two clocks generate the following two sample-rate groups:
- 44.1/88.2/176.4kHz
- 48/96/192kHz
The Off-Ramp 4 automatically adjusts the clocks for each sample-rate. Some software, such as Vista, Win7 or iTunes on Mac OS will not automatically change sample-rates to match the music file. For these it is important to manually change the sample-rate in the OS settings, or use a player software that overrides this and changes sample-rates automatically, such as Amarra, Pure Music or AyreWave on Mac.
Clock upgrades are available from the standard clocks. Two low-jitter standard clocks are provided unless you choose to upgrade to dual Turboclock. Turboclock is our best lowest jitter clock, which uses two Hynes voltage regulators. Turboclock takes the Off-Ramp 4 to a new level, well ahead of the competition.
USB cables
With the Off-Ramp 4 Asynchronous USB interface, the USB cable is less important. We have achieved wonderful results using the included cable or a Belkin Gold. Using more expensive cables may produce better results, but the jury is still out. We have not heard an obvious improvement yet. In theory, it should not make a difference.
Power
The Off-Ramp has a DC input power jack with 2.5mm pin. Center is positive. It is protected from reverse voltage. The included AC adapter is floating, but can be replaced with an adapter or linear supply with earth ground connected to negative. We recommend at least 1 amp @ 12VDC. The high-speed switching supplies used by Empirical Audio are critical to the performance of our products. They respond much more quickly to current demands than Linear supplies. Our regulators and internal filtering do a good job of eliminating any RF from the switching regulator power.
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. This 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.
I2S RJ-45 connector pinout
Pin 1 - SCLK
Pin 2 - SCLK return
Pin 3 - SDATA
Pin 4 - SDATA return
Pin 5 - L/RCLK
Pin 6 - L/RCLK return
Pin 7 - MCLK
Pin 8 - MCLK return
Specifications
Download User Manual
Inputs
- USB 2.0 from Mac or PC, up to 5 meter USB cable
- +12VDC power – AC Adapter included, or optional Monolith LI Battery Power Supply DC connector is 2.5mm pin, center positive. 1 Amp @ 12VDC minimum required
Outputs (all outputs are active)
- Isolated S/PDIF coaxial – either OFC RCA jack or 75 ohm Canare BNC jack
- AES/EBU – XLR male
- I2S on RJ-45, Empirical Audio standard (5V, optional 3.3V) output impedance is 120 ohms
Compatibility
The Off-Ramp 4 is designed to work with all 2-channel DACs and SS receivers/processors. It will not pass AC-3 surround-sound. It is compatible with Mac or PCs running XP, Vista or Win7. It works with most formats and players on PC and Mac, including Foobar, Jriver, Media Monkey, WMP, iTunes and Winamp. We do not recommend using iTunes on a PC, only Mac. For best results, we recommend Mac with an improved player software such as Amarra, Pure Music or AyreWave.
Output Performance
The I2S interface is generally superior to the AES/EBU and S/PDIF. The I2S is compatible with Empirical Audio DACs, Perpetual Technologies P-3A, Northstar DACs and the Stello DA100. The S/PDIF is generally superior to the AES/EBU, although this depends to some extent on your DAC. The very best S/PDIF, AES/EBU and I2S cables should be used to minimize the added jitter. With a good S/PDIF cable, this interface is very close to the I2S performance.
Included
- Off-Ramp 4
- 5 meter USB cable
- +12VDC AC adapter
- CDROM with PC/Mac installation software
Options
- Dual Turboclock upgrade
- Monolith Li battery supply
- I2S output options - contact us
Download Drivers
- Windows 7 / Vista
- Windows XP / 2003
- Mac OSX 10.6 Snow Leopard
- Mac OSX 10.5 Leopard
- Mac OSX 10.4 Tiger
Configure Your Off-Ramp 4
*USB software and firmware licensed from M2Tech