Benchmark ADC 1 24-bit/192 kHz A/D Converter

The long awaited Benchmark A/D converter companion to the DAC 1 is here in the form of the compact and versatile ADC 1. This two-channel unit supports sample rates up to 192 kHz via single wire AES/EBU XLR, S/PDIF BNC, and TOSlink optical connectors. Three fixed and three variable gain settings are settable on the front panel.
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INPUT SENSITIVITY

Fixed gain

20/10/0

1.22/3.84/12.2 V

4/14/24 dBu



Variable gain, controls full clockwise

20/10/0

0.153/0.467/1.55 V

- 14.1/-4.4/6 dBu



INPUT IMPEDANCE

At 1 kHz,

186 kilohms



INPUT OVERLOAD

Unit reaches digital full scale before input overload occurs at

N/A



OUPUT POLARITY

Digital output audio signal polarity relative to audio signal input

non-inverting



FREQUENCY RESPONSE

44.1 kHz Fs

+0.0, -3.0 dB 20 Hz - 21.1 kHz


96.0 kHz Fs

+0.0, -3.0 dB 20 Hz - 46 kHz


192.0 kHz Fs

+0.0, -3.0 dB 20 Hz - 91.4 kHz



TOTAL HARMONIC DISTORTION PLUS NOISE

At -1 dBFS, Measurement bandwidth = Fs/2,

44.1 kHz Fs

<= 0.00071% 20 Hz - 20 kHz


96 kHz Fs

<= 0.001% 20 Hz - 40 kHz


192 kHz Fs

<= 0.0013% 20 Hz - 80 kHz



LINEARITY ERROR

44.1/96/192 kHz Fs

< +/- 1 dB 0 to -130 dBFS

< + 4 dB @ -140 dBFS



SIGNAL TO NOISE RATIO

Input termination 600 ohm, noise relative

to 0 dBFS,

44.1/96/192 kHz Fs


Wide band (Fs/2)

118/114/109.4 dBFS


A weighted

120.5/120.2/119.8 dBFS


DYNAMIC RANGE

44.1/496/192 kHz Fs
A weighted,
<10 Hz - Fs/2 BW

118.2/118.1/118.3 dB



QUANTIZATION NOISE

44.1/496/192 kHz Fs
20 Hz @ 0 DBFS, THD+N
in 400 Hz - 20 lkHz BW

-116.2/-116.2/-116.1 dBFS



CHANNEL SEPARATION

44.1/96/192.kHz Fs
Ch1 > Ch2 & Ch2 > Ch1

20 Hz - 20 kHz > 100 dB



Note: Unless otherwise noted, all measurements are for the left channel, gain set for 20. Signal input was to the XLR balanced inputs.
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(click thumbnail)The long awaited Benchmark A/D converter companion to the DAC 1 is here in the form of the compact and versatile ADC 1. This two-channel unit supports sample rates up to 192 kHz via single wire AES/EBU XLR, S/PDIF BNC, and TOSlink optical connectors. Three fixed and three variable gain settings are settable on the front panel.

Measurements with a single-wire digital interface at the higher digital audio sample rates requires the latest Audio Precision test gear, namely the 2700 series instruments. My present Audio Precision System Two Cascade unit can only handle the high sample rates with the now obsolete two-wire interface. The West Coast Audio Precision representative, Jonathan Novick was kind enough to loan me his demo unit to enable me to measure the two higher sample rates of 176.4 and 192 kHz on the ADC 1. I am working on getting my own machine upgraded to handle the single-wire high sample rate interface for future digital audio products to measure for Pro Audio Review.

To keep the number of measurement files and data presentation to something reasonable, most testing was done at 44.1, 96 and 192 kHz sample rates.

Figure 1 shows the high frequency response rolloffs for the main sampling frequencies of 44.1, 48, 88.2, 96, 176.4, and 192 kHz. The presentation is from 10 kHz upwards to best see the high frequency end of the response. The low frequency response of the unit (not shown) was essentially the same for all sample rates and was down about 0.05 dB at 10 Hz.

In measuring distortion of the unit, there was a tendency for rising high frequency distortion, more noticeable at the higher gain settings and for the right channel. This was true for all sampling frequencies. The distortion residual was dominant second harmonic for both channels. Figure 2a shows the distortion vs. frequency at fs = 192 kHz for the left channel as a function of gain setting of 20, 10, & 0. In all cases the output level was Ð1 dBFS to avoid possible clipping artifacts. Figure 2b is for the right channel. The measurement bandwidth was Fs/2 for these figures. Figure 3 shows the lower noise floor (less bandwidth) of a similar plot for a 44.1 kHz sample frequency at Ð1 dBFS input level for left and right channels at the 20 gain setting. Distortion vs. level for a 1 kHz test frequency is shown plotted in figure 4 for sampling frequencies of 44.1, 96, & 192 kHz. For clarity, the left channel only is shown. Also noticeable, is the 0 dBFS distortion is higher at the two higher sampling frequencies The ultimate noise floor as distortion goes away with decreasing level is most a function of the sampling frequency and the resultant audio bandwidth, which in this case, was Fs/2, necessary for the measurements in the higher sampling frequencies.

Input/output linearity was quite good for the ADC 1 and was more or less the same for all sampling frequencies. A typical result is plotted in figure 5 for both channels and at a sample rate of 44.1 kHz.

Channel separation was essentially independent of sampling frequency but did vary a bit with the gain settings being a bit better at the lower gain settings. Still, better than 100 dB at 20 kHz is very good performance in this test. A plot of channel separation at the gain setting of 20 is shown in figure 6.