Bricasti Design M1 D/A converter Measurements

Sidebar 3: Measurements

I used Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system to measure the Bricasti M1 (see www.ap.com and the January 2008 "As We See It"); for some tests, I also used my vintage Audio Precision System One Dual Domain and the Miller Audio Research Jitter Analyzer.

The Bricasti's electrical inputs successfully locked to datastreams with sample rates ranging from 44.1 to 192kHz; the TosLink input would not lock to datastreams with sample rates greater than 96kHz, which is normal. As supplied for review, the M1's maximum output level was 4.3V from the balanced XLR jacks and 2.01V from the single-ended RCAs, sourced from output impedances of 58 and 29 ohms, respectively, at all frequencies. Both sets of outputs preserved absolute polarity (ie, were non-inverting), the XLRs being wired with pin 2 hot.

I examined the impulse response of each of the seven filters by feeding the M1 digital black data into which I had inserted a single sample at full scale. The filters all had similar time-symmetrical, linear-phase impulse responses; fig.1 was taken with Filter 4. However, the filters did differ in their frequency-domain behavior. Fig.2 shows the response of Filter 1 with data sampled at 44.1kHz (green and gray traces), 96kHz (cyan, magenta), and 192kHz (blue, red). This filter has a sharp rolloff just below 20kHz with 44.1kHz data, though the higher sample rates follow the gentle rolloff seen above 10kHz. Both 96 and 192kHz roll off earlier than with other D/A processors, the responses being –3dB at 33 and 55kHz, respectively. Fig.3 shows the behavior of Filter 4. The 96 and 192kHz responses are identical to Filter 1, but some passband ripple is now evident at 44.1kHz. This is generally felt not to be a good thing, but John Marks actually preferred the sound of Filter 4 to the other six. Fig.4 shows the response of Filter 6, which I preferred, while fig.5 shows the response of Filter 0, which neither of us liked but which gives the widest bandwidth at all sample rates.

Fig.1 Bricasti M1, Filter 4, impulse response (4ms time window).

Fig.2 Bricasti M1, Filter 1, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red). (0.25dB/vertical div.)

Fig.3 Bricasti M1, Filter 4, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red). (0.25dB/vertical div.)

Fig.4 Bricasti M1, Filter 6, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red). (0.25dB/vertical div.)

Fig.5 Bricasti M1, Filter 0, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red). (0.25dB/vertical div.)

The M1's channel separation (not shown) was superb, at >125dB in both directions below 1kHz and still 113dB at the top of the audioband. For reasons of consistency with the digital tests I have performed since 1989, my first test of a processor's dynamic range is to sweep a 1/3-octave bandpass filter from 20kHz to 20Hz while the processor decodes a dithered 1kHz tone at –90dBFS. The results of this test are shown in fig.6: with 16-bit data (top pair of traces), all that can be seen is the spectrum of the dither noise used to encode the signal. With 24-bit data (middle pair of traces), the noise floor drops by 20dB, implying that the M1 has almost 20 bits' worth of dynamic range, easily enough to allow the decoding of a dithered tone at –120dBFS (bottom traces). This is excellent performance, and, just as important, the lowering of the noise floor with the greater bit depth has not unmasked any supply-related spuriae. FFT analysis confirms this excellent resolution (fig.7), and no harmonic distortion components can be seen, though a supply component at 180Hz is now evident in the left channel at a roots-of-the-universe –137dBFS!

Fig.6 Bricasti M1, 1/3-octave spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS, with: 16-bit data (top), 24-bit data (middle), dithered 1kHz tone at –120dBFS with 24-bit data (bottom). (Right channel dashed.)

Fig.7 Bricasti M1, FFT-derived spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS, with: 16-bit data (left channel cyan, right magenta), 24-bit data (left blue, right red).

Looking at how the Bricasti's noise floor changed with differences in signal level, nothing was evident other than what could be attributed to the Audio Precision's gain-ranging circuitry (fig.8). Similarly, all that could be seen in the graph of the M1's linearity error was the recorded dither noise, so I haven't shown it. With its very low background noise and excellent linearity, the Bricasti's reproduction of an undithered tone at exactly –90.31dBFS was superbly symmetrical; the three DC voltage levels and the Gibbs Phenomenon "ringing" on the waveform's leading edges were all cleanly defined (fig.9, footnote 1). With undithered 24-bit data, the result was a good representation of a sinewave, despite the very low signal level (fig.10).

Fig.8 Bricasti M1, spectrum of 1kHz sinewave, DC–1kHz, at 0dBFS (left channel blue, right red), –60dBFS (left cyan, right magenta), –90dBFS (left green, right gray). (Linear frequency scale.)

Fig.9 Bricasti M1, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).

Fig.10 Bricasti M1, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit data (left channel blue, right red).

Harmonic distortion into high impedances was very low, and predominantly the third and fifth harmonics (fig.11), these respectively lying at –110dB (0.0003%) and –119dBFS (0.0001%). These odd-order harmonics rose by 10dB into the punishing 600 ohm load (fig.12), and were joined by the second and fourth harmonics—but in absolute terms, they are all still very low in level. The Bricasti's performance in the high-level, high-frequency intermodulation test depended on which reconstruction filter was selected. The levels of the difference tone at 1kHz and the higher-order intermodulation products at 18 and 21kHz were the same with all filters and were all very low in level, but the best rejection of ultrasonic images of the 19 and 20kHz tones was with Filter 0 (fig.13), the worst with Filter 4 (fig.14). Although a couple of aliasing products are visible in the audioband with Filters 4 and 6, these are still at –130dB or lower and are therefore inconsequential.

Fig.11 Bricasti M1, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

Fig.12 Bricasti M1, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 600 ohms (left channel blue, right red; linear frequency scale).

Fig.13 Bricasti M1, Filter 0, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

Fig.14 Bricasti M1, Filter 4, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

The Bricasti M1's rejection of jitter was one of the best I have measured; any jitter-related spuriae lay below the resolution limit of the Miller Analyzer. The cyan and magenta traces in fig.15 show the spectrum of the M1's analog output while it decoded a 16-bit version of the diagnostic J-Test signal via its TosLink input. The spectral lines visible are the residual odd-order harmonics of the low-frequency squarewave; these are not accentuated in any way, nor are any other sidebands visible other than a single pair at ±180Hz, these lying at almost –140dB. With the 24-bit version of the J-Test (blue and red traces), all the squarewave harmonics have disappeared, and the central spike that represents the 11.025kHz tones has narrower skirts. Jitter rejection was just as impressive via the M1's AES/EBU and S/PDIF inputs.

Fig.15 Bricasti M1, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit data via TosLink from AP SYS2722 (left channel cyan, right magenta), 24-bit data (left blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Bricasti Design's M1 has state-of-the-art measured performance.—John Atkinson



Footnote 1: The significance of this test is that in the 2s-complement encoding used in the Compact Disc, the transition from 0 to +1LSB involves just the LSB changing value, while the transition from 0 to –1LSB involves all 16 bits changing value. It therefore offers a quick way of identifying bit-magnitude errors (though with modern delta-sigma D/A converters, such errors are very rare).
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Bricasti Design Ltd.
123 Fells Avenue
Medford, MA 01255
(781) 306-0420
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COMMENTS
Erranti's picture

Hi there John,

Thanks for another informative and thorough review. I've turned to computer audio, or as it is also called, desktop audio. This is mainly to economize space and of course money. I have recently acquired a pair of Beyerdynamic T1s to upgrade from my AKG K702s, and I would also like to find a good headphone amplifier that can deliver what it takes to make these 600Ohm babies sound their best. 

I have been doing some online window shopping and research, and I have come across at least 4 very intersting Amps that according to their specs could do a very good job with the T1s, and which have still to be featured at Stereophile. Two of them feature DA converters that also have impressive specs.

The first candidates are German made Violectric V100 and V200, which can be obtained with built-in 16/48 or 24/96 DA converters via USB. Violectric also features a standalone DAC, the V800, which is a very versatile unit with some really serious specs. They are all very fairly priced and fabulously well built, and only with German components and labor.
http://www.violectric.de/Pages/en/products/index.php

The second candidate is both a headphone Amp and pre-amplifier. It's Headamp's GS-1, which is also a very well built Amp with great specs and fully manufactured in the US. 
http://www.headamp.com/home_amps/gs1/index.htm

The third candidate is the D2 DAC -and also headphone amplifier- by Anedio, which features some really fantastically good and detailed specs. 
http://www.anedio.com/index.php/audio/gandalf

I have read your reviews of Benchmark Media's USB DAC1 Pre, Grace Design's m903 and CEntrance's Dacmini CX, which are all great products, but I would still love to see any of these other components, which also feature great specs and appear to equal or challenge the DAC 1, m903 and Dacmini CX's performance.

In the case that these components are not within near future review plans, I would still appreciate any impressions you could have on them. Thanks in advance for your help,

Greetings, 

Erranti

Dan Moroboshi's picture

Dear JA,

since you reviewed this wonderful product of audio engineering, Bricasti releases an update extensive to the existing products which includes USB asynchronous interface and digital level control.

I would like to suggest a follow up using this USB interface and maybe measurements on this one.

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