Computer audio newbie? Don't panic. Start here.
With the new S/PDIF Bridge from Halide Design, it is possible to get a high resolution, ultra low jitter digital audio signal straight from your computer, with a single, plug-and-play cable.
Completely plug-and-play on both PC and Mac, the Bridge allows for 24 bit resolution at sampling rates up to 96 kHz, and works with virtually any file type and player.
The Bridge is build upon the solid foundation of the sophisticated USB audio receiver code, Streamlength™, by Wavelength Audio. Streamlength™ allows the extremely low phase noise clocks inside the Bridge to run as the master audio clock, resulting extraordinarily low jitter output. Since there is no resampling or reclocking, the footprint of the circuit becomes tiny - the Bridge runs smarter, not bigger.
Inside, highly filtered ultralow noise power regulation provides clean power rails for the internal circuitry. A high quality output transformer further isolated the output signal from any computer noise.
The goal of any S/PDIF converter is to convey the exact bits in the audio signal, with the least amount of jitter possible. Pretty much all S/PDIF devices can deliver the correct bits, although it is important that the device have the resolution needed to play the file. However, the timing is a different matter. Timing errors in the signal can come from a number of different sources: noisy power supplies or clocks, timing errors already present on the audio signal being encoded, and noise in the transmission line, just to name a few.
Most S/PDIF receiver devices will add at least some jitter reduction, especially in the higher frequencies, since the PLL (phase-locked loop) circuitry used to recover the signal typically requires filtering in order to work. In addition, some more advanced digital to analog converters incorporate additional reclocking circuitry, which reduces the jitter noise throughout the audio band. However, a typical S/PDIF receiver usually has little or no jitter attenuation throughout the audio band and below, meaning much of the audible jitter in the incoming signal is simply passed into the output digital signal (typically a three-line audio signal, such as I2S or right-justified).
Still, attenuation of high frequency jitter is not perfect, and there is always a lower frequency limit below which the reclocking circuitry will not work. For these reasons, it is critical the the S/PDIF signal itself have very low timing deviation, through and below the audio band.
USB Receiver: The Bridge is based around the sophisticated USB receiver code, Streamlength by Wavelength Audio. The Streamlength firmware, running on the TAS1020B, allows for several key advantages:
The last feature, which is frequently referred to by the technical name "asynchonous" (as opposed to "isosynchronous"), is the key to obtaining ultra-low jitter on USB devices. With asynchonous USB receivers, the jitter is essentially limited only by the clocks on the audio device, plus any [typically very small] timing errors from additional logic gates that the clock signal must travel through.
Power Supply: Critical to any high-end audio design is the power supply. Since the Bridge is powered through the USB connection, the power coming from the computer is supplied at 5 volts, though is typically not terribly clean, due to noise in the computer and other attached peripherals, such as hard drives.
In order to supply clean power to the on-board circuitry, the Bridge uses a combination of power supply filtering and an newly released power down regulater. Power coming into the device is first PI filtered (CLC), which gives a two-pole attenuation for noise above roughly 3kHz. This works to eliminate high frequency noise, which down-regulators are typically not as good at rejecting. This filtered signal, which is slightly less than 5V (due to resistive elements in the passive filter), is down regulated to 3.3V for the digital electronics, and a separate 3V line for the clocks. Note that down-regulators tend to be excellent at rejecting noise at DC and lower frequencies, the rejection ratio falls off at higher frequencies.
The combination of an initial LC filter and a regulator with high PSRR (70dB at 10 Hz, a reduction factor of over 3,000), ultralow noise regulator insure that the clocks and the digital circuitry can operate as accurately as possible.
S/PDIF encoding and output stage: The output from the TAS1020B is in I2S, which is converted to the bi-phase encoded (S/PDIF) format with a S/PDIF transceiver chip. In order to insure that the chip has not added any jitter, the output from this device is clocked a final time by the original master clock of the system, using a D-type flip-flop
Output Transformer: In order to isolate the output from the (potentially noisy) computer ground, and to avoid the possibility of ground loop noise, SPDIF commonly employs an output transformer. We use a small, high-quality output transformer, which allows excellent isolation and signal integrity in a small package.
Physical construction: A key feature of the Bridge is the small size. The small size wound up being somewhat of an after-thought in design - the original plan was to build the best possible circuit, and it turns out that we were able to build it quite small. Much of this has to do with the use of Streamlength. Because the core components are quite small and require no additional jitter reduction circuitry (such as asynchronous resampling), which can take up quite a bit of board space, the entire device can be built into the plug.
The enclosure is custom manufactured by CNC from high quality aluminum. The BNC connector version is a standard 75 ohm BNC connector (gold pin, of course), custom milled so it can connect to the enclosure during assembly. Alternatively, the device is available with an Eichmann Silver Bullet RCA connection.
“"The Bridge To Sonic Bliss? Simply put, I was surprised by the high performance of The Bridge. I had an inkling The Bridge would be good based on its designers and the Streamlength™ USB code, but I didn't expect it would be this good. Playing all types of music The Bridge offered wonderful separation of the instruments and a clarity from top to bottom that was close to my Lynx AES16 PCI card.
Listening to [Michael Daugherty's] Niagara Falls through The Bridge seemed to open another complete octave at the top end compared to other USB to S/PDIF devices I have used. The resolution and extension was so good I contacted a couple colleagues in the industry to discuss why I wasn't getting this level of performance from other converters. Specifically the M2Tech hiFace.
The Halide Design Bridge asynchronous USB to S/PDIF converter has earned a well deserved spot on the Computer Audiophile Suggested Hardware List. This simple, small, single cable solution incorporates innovative design and the current holy grail of USB implementations – asynchronous transfer mode. There are some fabulous DACs around without USB or FireWire input that will benefit greatly from the Halide Design Bridge. I highly recommend The Bridge from Halide Design." – Computer Audiophile
“Plugging the Bridge into my music PC was an uneventful as could be, just the standard bit about installing new hardware and after a few seconds Windows pronounced it ready for use . . . presto, I had music. And the music was lovely, right out of the box and with no tweaking I could tell this was going to be enjoyable.
Sitting down to listen a few days later confirmed the first impression, still lovely and very musical. The greatest praise I can offer is there was no desire to remove it from the system and put something else in and that is exactly the case, it stayed in the system for the next few weeks and was the source of much musical enjoyment. When trying come up with some descriptions of the sound my notes are filled with items such as focused, nice bass, lovely bass, lovely background vocals, nicely delineated sound stage, great pace and flow, nice depth, great tone. I think you get the picture, the system sounded fabulous with the Halide Bridge. Unfortunately the hiFace Evo had to leave just as the Bridge arrived so there was no opportunity for comparison; I think they would have been very close in performance . . . the Bridge is a little less expensive AND eliminates the need for an S/PDIF cable and a USB cable. Overall I found the Bridge to be very nice and would not hesitate to recommend it, especially for those less computer savvy as almost no configuration is required.” – Enjoy the Music.com
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