SCHIIT BIFROST MULTIBIT DAC
A high-value, high-performance DAC designed for PCM signals up to 24 bits and 192kHz that’s upgradeable?
Remember when the first two CD players appeared on the market? The Sony offering was a 16-bit unit, albeit with a DAC that switched between each channel, misaligning them by a small amount. (*See footnote.) Philips, though, felt that 16-bit DACs weren’t sufficiently accurate at that point, so it launched with a 14-bit DAC. The inherent 12dB higher noise floor resulting from that 2-bit shortage still put it below the noise floor of just about any phono pre-amplifier available at the time.
The problem was linearity. Was it possible to create a circuit that could accurately reconstruct analogue signals from digital numbers which spanned four orders of magnitude? That issue soon became moot by means of a nifty bit of side-stepping. As silicon got better (hey, compare the capabilities of a modern computer with an early 1980s model: it’s at least three orders of magnitude faster and more powerful). Instead, oversampling and delta-sigma conversion became the norm. In effect these turn PCM to something like Direct Stream Digital, allowing for a very simple final DAC stage. (Yes, there are additional complications.) This also dealt with the complexities of creating an extremely sharp anti-aliasing filter, and the drawbacks of such filters.
I bring all this up because the Schiit Bifrost DAC reviewed here—a high-value, high-performance DAC designed for PCM signals up to 24 bits and 192kHz sampling—is the Multibit version.
The standard Schiit Bifrost DAC ($649) uses the Asahi Kasei AK4490, a 256× oversampling delta-sigma DAC chip. The review Schiit Bifrost Multibit model is $979 and uses a very different DAC technique. Since the Bifrost is upgradeable, you can convert the former to the latter, but the board will cost you $549. This is not a user upgrade. Your Bifrost will need to go back to the distributor for installation, and the necessary firmware upgrade for the motherboard.
The only visual differences between the Bifrost and the Bifrost Multibit are stickers, one on the box and one on the back panel of the unit.
I will return to the Multibit thing shortly, but first a little about the unit. It’s a mid-sized (229×58×172mm), three input model that weighs 2.3 kilos. There’s a USB Type-B socket which you use with a computer (or, if you’re that way inclined, a smart phone) to turn digital audio into analogue, plus an optical input and a coaxial digital audio input. All three support the resolution mentioned—192kHz, 24 bits. There is no support for Direct Stream Digital (neither, apparently, is there in the basic Bifrost, even though its DAC chip supports up to quad speed DSD). Output is via standard RCA sockets. The top, bottom and front of the case are formed from one folded sheet of 3mm aluminium.
It provides high performance and excellent value for money for those who don’t need DSD capabilities...
Three small indicator lights on the front indicate which input has been selected, while a button cycles through the inputs. There are no indicators for showing sampling frequency, so unless you’re using audio software that makes a positive statement about what is being delivered to the DAC, you’ll be proceeding somewhat on trust that you have your computer configured correctly and it is not resampling the audio. A small hard-wired switch on the back turns the power on and off. The FAQ in the slim manual says that you can leave the Bifrost switched on ‘all the time’.
That manual (and the Schiit website) are rather cute. On the back cover next to the company name is a tag line: ‘It Happens’. It notes of the seeming ventilation holes on the top that they ‘Don’t Go Through’, saying: ‘Hey, you try getting FCC-friendly radiated noise on a DAC that has vents in the cover. Go ahead, try. But hey, they look cool, right?’ I confess to having a soft spot for a company that doesn’t take itself too seriously.
What is serious is the technology inside. Instead of an off-the-shelf audio DAC chip, Schiit has gone for an industrial chip, not designed at all for audio applications, and has built its own circuitry around it. Schiit is very up front about this. It describes the system as using ‘Schiit’s proprietary closedform, time- and frequency-domain optimised DSP-based digital filter… coupled to a precision Analog Devices AD5547CRUZ digital-to-analog converter—a D/A never before used in any other audio product.’
Is this some form of heresy? Shouldn’t a high-quality audio device use components designed for audio products? The data sheet for the AD5547 (Rev.D) suggests as applications test equipment, instrumentation, digitally controlled calibration and digital waveform generation.
It seems to me Schiit isn’t treating digital audio signals as being imbued with some magical musical essence that will be lost without uncertain, golden-eared hand-tuning. No, it’s treating them as things to be converted as accurately as possible into the original analogue signals from which they were formed. It is bringing engineering to bear on that task.
The AD5547 is an R-2R ladder-based DAC chip. That is, good old fashioned technology, but capable of extreme precision thanks to the three-and-a-half decades of development since those early CD players. Since the chip is a 16-bit model, and the DAC is rated at supporting 24-bit signals, I’m guessing that some oversampling still comes into play. The chip actually has a bandwidth of 6.8MHz. But that’s pushing the bounds of my comprehension. What magic this ‘ proprietary closed-form, time- and frequency-domain optimised DSPbased digital filter’ pulls off, we’ll see in the test results.
Schiit rates the frequency response of the Bifrost Multibit at 20Hz to 20kHz ±0.1dB, and 2Hz to 150kHz ±0.5dB. The output is rated at 2 volts RMS. THD is rated at less than 0.005% across the full audio bandwidth, while IMD is rated at less than 0.008% and the signalto-noise ratio is rated at greater than 109dB (referred to 2 volts RMS).
Finally, I will note that Schiit has made its DACs modular and upgradeable. So should there be significant improvements available in the future in either the digital or analogue sections, the internal components can be changed. This, again, would be a job for the distributor. Schiit would like its customers to note however, that although the Bifrost has a 5-year warranty, this covers only labour and parts in the unlikely event that a repair is required: it does not entitle you to upgrades.
In use AnD lIstenInG sessIons
As seems to be now standard, no drivers were included in the box. The manual—presumably not too recent a publication—says to go to a specific link on the manufacturer’s website to install them.
But you may not need drivers anyway. Macs have supported USB Audio Class 2 for ages, and so (belatedly) has Windows, since early 2017. The driver page says: ‘Most newer Windows versions already have drivers for our stuff.’ I found that Windows support unsatisfactory when first introduced, but whether it’s this particular DAC, or the several Windows 10 upgrades since then, there were no problems this time. I plugged the Schitt into my desktop computer and instantly the usual USB ‘device connected’ sound emerged from the (already powered up) speakers. I checked the Windows Manage Audio Devices dialog box, and there it was, set as the default device.
So I fired up Foobar 2000, went to its output settings and found the Schiit listed there with three options. ‘DS: Speakers (Schiit USB Audio Gen 2)’, ‘WASAPI (event): Speakers (Schiit USB Audio Gen 2)’ and ‘WASAPI (push): Speakers (Schiit USB Audio Gen 2)’. The first of those simply runs the sound through the standard Windows audio processes, and will resample it if necessary to match the output sample rate you’ve set in the Windows dialog. For hi-fi listening, this is best avoided, but is useful to have if your machine is a general-purpose computer and you need to hear notifications and such.
But for the best performance, you’ll want one of the WASAPI settings. WASAPI stands for Windows Audio Session Application Programming Interface. The standard Windows audio handling has to mix your music with beeps and buzzes from your system, audio from YouTube videos and all that stuff.
What is serious is the technology inside. Instead of an off-theshelf audio DAC chip, Schiit has gone for an industrial chip not designed at all for audio applications
Graph 4. Noise at 96kHz/24-bit re 2V. USB input–Windows (white trace) vs. Optical Input—MAC (green trace) vs. Optical Input–MAC but with USB input disconnected (blue trace).
Graph 1. Frequency response (44.1kHz/16-bit). Left channel (white trace) vs. right channel (green trace).
Graph 2. Frequency response (96kHz/24-bit). Left channel (white trace) vs. right channel (green trace)
Graph 3. Frequency response (192kHz/24-bit). Left channel (white trace) vs. right channel (green trace).
Schiit has made its DACs modular and upgradeable. So should there be significant improvements available in the future, the BiFrost can be upgraded