This is only a preview of the September 2021 issue of Practical Electronics. You can view 0 of the 72 pages in the full issue. Articles in this series:
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Part 1 –
By Phil Prosser
USB
• 192kHz
• 24-bit
This beauty is the ultimate in high-fidelity audio recording and playback.
You could use the SuperCodec for digitising LPs, recording your own music
or playing music with a very high-quality stereo amplifier driving excellent
speakers. It can also turn your PC into an advanced audio analyser, capable
of measuring harmonic distortion down to 0.0001% and signal-to-noise
ratios up to 110dB (or even more, with suitable attenuators).
T
his project was inspired by
a reader who wanted to digitise
his LP collection, and asked
us if we had a USB sound interface
that would let him record with very
high fidelity.
If you want better quality audio for
your PC, including the ability to record
and playback at high sampling rates
and bit depths (up to 192kHz, 24-bit),
then read on.
In addition to recording and playback of music or other audio, this
project enables your PC to become an
advanced audio quality analyser. You
just need the right software; we’ll get
to that later.
With the addition of the 2-Channel
Balanced Input Attenuator for Audio
Analysers and Digital Scopes from the
May 2016 issue, you will have a potent
measurement tool indeed.
16
It allows you to measure the distortion performance of the very best
amplifiers, preamps, equalisers and
other audio devices.
In designing this project we started
by looking for a simple IC CODEC as
the solution. There are some all-in-one
USB audio chips available, but they
fall short on several fronts. They generally limit you to the use of 48kHz, 16bit audio, but more importantly, they
generally have quite high distortion
figures of around 0.1%, with signal-tonoise ratios topping out at about 85dB.
We need better performance than that.
The first prototype for this project
used the same analogue-to-digital converter (ADC) and digital-to-analogue
converter (DAC) boards from the DSP
Active Crossover (Jan-Mar 2020).
Those boards use the Cirrus Logic
CS5381 and CS4398 chips respectively.
While they are a few years old, their
performance is phenomenal. The
CS4398 DAC has a dynamic range of
120dB and signal-to-noise ratio (SNR)
of 107dB; the CS5381 ADC achieves
an SNR of 110dB, or 0.0003%.
So we decided to stick with those
chips but put as much as possible onto
one board, to make it easier to build
and give a nice, compact result. The
performance this USB sound card
delivers should fulfil even the most
ardent Hi-Fi enthusiasts’ desires.
We did make several changes and
improvements compared to that earlier
project, though. This design teases the
maximum performance from these
parts, in a ‘no-compromise’ approach
to low noise and low distortion.
Plus, it provides ‘plug-and-play’
operation for Windows, Mac and
Android computers. We tested it on
Practical Electronics | September | 2021
Windows, but trust the vendor’s promise of Mac and Android compatibility.
During the development process, we
made several key decisions:
To get the best performance, we need
to isolate the PC’s ground from the
USB sound card. Computers are
noisy things, so we must break the
ground loop.
It must be supported by proper drivers in Windows and ideally, all other
common operating systems.
The ability to handle different sampling rates is important, though once
set, it will generally be left alone.
The PCB layout must minimise
noise, plus we need to be able to
connect the inputs and outputs in
a variety of ways.
Putting a transformer in the box
would introduce measurable 50Hz
related noise, even if we took measures to minimise it. Since we don’t
want a complicated power supply arrangement, we chose a DC plugpack.
For the neatest/cleanest project for
PE constructors, everything should
be on one PCB.
As we have noted in the past, the use
of some surface-mount components is
unavoidable in projects like this. We
need to use specific parts to get this
level of performance, and in many
cases, they only come in SMD versions. In this case, that includes the
USB interface and the ADC and the
DAC chips.
Where possible, though, we have
used through-hole components. This
has resulted in the PCB being a bit
larger than an all-SMD version would
be, but we have found a very nice case
that fits it neatly.
Principle of operation
Fig.1 shows the block diagram of the
SuperCodec. It consists of a USB-toI2S (serial digital audio) interface with
galvanic isolation to the remainder of
the circuit, a local clock generator for
Features
Stereo input and output with very low distortion and noise
Connects to computer via USB
Windows, macOS and Android driver support
Asynchronous sampling rate conversion (completely transparent)
Full galvanic isolation between computer and audio connectors
Housed in a sleek aluminium instrument case
Power by 12V DC (eg, from plugpack)
Power and clipping indicator LEDs.
the ADC and DAC with bidirectional
asynchronous sampling rate conversion (ASRC), the power supply section and the aforementioned ADC and
DAC sections.
We have chosen to use a MiniDSP
MCHStreamer to provide the USB interface. This is a pre-built device that
we have integrated into our design.
This avoids us having to develop
the hardware and USB driver software
for the PC which is complex, expensive and needs to be done very well
to deliver you an easy-to-use product.
It is essential that constructors can
reliably install the sound driver software for this project and have it work
with a minimum of fuss. The investment in this component is well worth
the ease of use it will deliver for you.
This project appears to a Windows
computer as a sound interface that you
select and use just like any other – we
show you how to in the box titled
Setting up the MCHStreamer. This is
essentially a regular audio device then,
just one of very high quality.
The MCHStreamer is a very clever
device that can provide 10 input and
output channels (five stereo pairs)
with sampling rates of 32-384kHz at
24 bits. It supports I2S as well as TDM
and other audio formats.
We are using it as a two-channel
(stereo) audio interface. This leaves
many channels unused, but that is not
the aim of this project. If you want to
use this design as the basis of a multichannel recorder, be our guest!
The MCHStreamer is powered from
the USB cable and breaks out the I2S
audio interface that we need on a pair
of headers.
The chip we’re using for galvanic
isolation requires a power supply
on both sides of the barrier. Luckily, the MCHStreamer has a 3.3V
output available on an expansion
header which we can use to power
the computer-side of that chip. The
audio-side power supply is derived
from the plugpack, along with power
for the rest of the circuit.
You can buy the MCHStreamer
from: https://bit.ly/pe-sep21-mch –
once you register and order it, you
can download the PC driver software.
We have laid out our sound card so
that the MCHStreamer plugs straight
onto the underside of the board. This
avoids having to send high-speed
digital signals over a ribbon cable.
When purchasing parts for this, be
very careful to get the header specified in the parts list. Any alternative
needs a pin pitch of 2mm and a
minimum height of 10mm; otherwise,
you will not be able to seat the MCHStreamer fully.
Performance measurements
We used three methods to measure the
performance of the USB SuperCodec,
and these measurements aided us in
improving it over several iterations
until we arrived at the final design.
The first method was to feed in a
very-low-distortion sinewave from a
Fig.1: the concept of the USB SuperCodec is deceptively simple, since much of the complexity is hidden in the prebuilt MiniDSP MCHStreamer module. That USB interface module produces a serial digital audio stream which passes
through a galvanic isolation section and onto the ASRC, then the separate ADC and DAC sections. It’s all powered
from the PC USB 5V and a 12V DC plugpack.
Practical Electronics | September | 2021
17
Fig.2: spectral analysis (large window FFT) of the data
from the SuperCodec’s ADC when fed a sinewave from a
Stanford Research Ultralow Distortion Function Generator.
This gives an excellent result of 0.0001% THD (−121.4dB).
That’s despite an earth loop causing a larger-than-normal
spike at 50Hz, which was fixed with some extra isolation in
the final version of the sound card.
Fig.3: a close-up of the 980-1020Hz portion of the spectral
analysis, showing very little evidence of clock jitter in the
ADC system. That’s because the crystal oscillator, digital
isolators and ASRCs are all low-jitter devices. High jitter
can distort signals since the sampling rate effectively
changes between samples.
Stanford Research DS360 Ultralow
To verify that clock jitter is not a Loopback testing
Distortion Function Generator. Very problem, we then ‘zoomed in’ to the The second test method was to conlarge sample sets were run through 1kHz fundamental, as shown in Fig.3. nect the unit’s outputs to its inputs
an FFT so we could
via a stereo RCA-RCA
inspect the close-in
cable. This lets us
Specifications
phase noise.
conduct ‘loopback’
Sampling rate: 32-192kHz
The reason for dotests using PC audio
Resolution: 16-32 bits (24 bits actual)
ing this (rather than
analysis software. The
Loopback total harmonic distortion (THD): 0.0001% (−120dB)
merely looping the
result of the first such
output back to the
test is shown in Fig.4.
DAC THD+N: 0.00050% (−106dB)
input) is that we need
You can see that we’ve
ADC THD+N: 0.00063% (−104dB)
independent clocks
solved the earth loop
Loopback THD+N, no attenuator: 0.00085% (−101.4dB)
for the signal generanow as the 50Hz peak
Loopback THD+N, 8dB resistive attenuator: 0.00076% (−102.5dB)
tor and ADC to pick
is at −130dB! You can
Recording signal-to-noise ratio (SNR): 110dB
up any distortion
also see the 50kHz
Playback SNR: 107dB
caused by clock jitter.
spike from the switch Dynamic range: 120dB
With both devices
mode circuitry.
Input signal level: up to 1V RMS
running off the same
Importantly, there
Output signal level: up to 2.4V RMS; 2.0-2.2V RMS
clock, those effects
is no spike at 25kHz,
(−1.5 to −0.75dB) for best performance
are liable to cancel
12.5kHz or related freeach other out, at
quencies, suggesting
least partially.
that the switchmode
The results of this first test are This plot shows spectral data for 1kHz regulators are not squegging – ie, are
shown in Fig.2. Note that we had an ±20Hz. This shows that the fundamen- free from subharmonic oscillation that
earth loop during this test, leading tal is 120dB down at about ±2Hz from could affect audible frequencies.
to a greater than usual spike at 50Hz the fundamental. That’s about as good
The harmonics of the very slightly
(this was fixed later); despite this, as you can expect, and suggests that distorted 1kHz fundamental are visthe reading is extremely promising jitter in the clock source and digital ible at 2kHz, 3kHz... up to 8kHz, then
with a THD figure of just 0.0001% signal path is minimal and has little 11kHz and 12kHz. The strongest hareffect on performance.
(−118dB) THD.
monic is 2kHz (second harmonic), at
Fig.6: the noise floor of the complete DAC+ADC system.
Although it is higher than the ADC alone, it is still very low
at around −130dB.
18
Fig.7: here the 1kHz test signal has been reduced in amplitude
by 10dB, dropping from around 1V RMS to around 0.1V
(100mV) RMS. That’s below most normal ‘line level’ signals,
but despite this, distortion performance is still excellent, with
THD measuring as −112dB/0.0002%.
Practical Electronics | September | 2021
Fig.4: the first loopback test, measuring the performance
of the complete DAC+ADC system. Performance is still
excellent with only slightly higher harmonic distortion than
the ADC alone, at −118dB (still rounding to 0.0001%).
Fig.5: the noise floor of the ADC, measured with the inputs
shorted. The biggest spike in the audible range is at 50Hz
due to mains hum pickup, but this is hardly a problem,
being below −140dB.
Total Harmonic Distortion (%)
around −118dB. The result is a very Indeed, if you are using this device
We made many other loopback
low THD figure of −118dB/0.00013%. as part of a measurement system, you measurements at other test frequencies
Remember, that this now includes would need resistive dividers, espe- ranging from 20Hz up to 19kHz, all
any distortion from the DAC plus the cially if the device you are measuring with virtually identical results, so the
plots are not worth reproducing. We
ADC, so this is very impressive. But has gain (eg, an audio amplifier).
also ran 1kHz tests with lower
this measurement does not
and higher signal levels.
include noise.
Fig.7 shows the results
To calculate the THD+N
with the output level refigure and signal-to-noise
duced by 10dB. This only
ratio, the inputs to the ADC
increases the THD figure to
were shorted out, and a new
−112dB/0.0002%, indicating
spectrum captured (Fig.5).
that you aren’t sacrificing
We then reinstated the loopmuch performance by operatback cables and measured
ing the codec at lower signal
the input level with the DAC
levels when necessary.
silent (Fig.6). These give us an
Fig.8 is at the maximum outidea of the noise floor, which
put signal level, which increasis around −104dB for the ADC
es second and third-harmonic
alone and −102dB for the
distortion so that the THD
DAC+ADC. Both figures are
figure is −111dB/0.0003%.
limited by 50Hz hum pickup.
This indicates that the optimal
Since these levels are The back end of the SuperCodec has all the input and
output connectors (the RCA sockets) along with the USB
signal level for low distortion
significantly higher than the
connector and the 12V DC power socket.
is a few decibels below maxiTHD alone, that means the
So when used as a measurement sys- mum. But you’ll still get decent results
THD+N performance figures for the
sound card are determined just by the tem, expect slightly better performance at the maximum output signal level, if
than the figures given here suggest. Es- that’s what you need.
noise levels.
By the way, since the DAC has to sentially, the loopback
have its output level set no higher than THD+N (and thus the
SuperCodec DAC THD+N vs Frequency 19/05/20 14:37:19
.01
−7.5dB to avoid overloading the ADC in measurement limit) will
approach the 0.00063%
22kHz BW 0dB
the loopback test, we could have gotten
22kHz BW -1dB
.005
better results by inserting a resistive (−104dB) figure given
22kHz BW -2dB
divider between the output and input. for the ADC alone.
22kHz BW -7.5dB
80kHz BW 0dB
.002
.001
.0005
.0002
.0001
Fig.8: the 1kHz test signal has been increased to the
maximum DAC output level of a bit more than 2V RMS. You
can see that in this case, more isn’t necessarily better, as the
THD figure is slightly worse than the 1V test case, yielding a
THD figure of −111dB/0.0003%. That’s still excellent, though!
Practical Electronics | September | 2021
20
50
100
200
500 1k
2k
Frequency (Hz)
5k
10k
20k
Fig.9: THD+N (not THD) at four different signal levels
for the SuperCodec’s DAC, asFig.9
measured with our Audio
Precision System Two. The fifth curve has a wider
measurement bandwidth of 20Hz-80kHz, to get a more
realistic idea of distortion levels at higher frequencies.
Unfortunately, measurements with 80kHz bandwidth
also have an unrealistically high noise level.
19
Parts list – USB SuperCodec
1 PCB assembly – see below
1 Hammond 1455N2201BK extruded aluminium instrument case
with black panels [Altronics H9125, Mouser 546-1455N2201BK]
1 MiniDSP MCHStreamer USB-to-I2S interface
[https://bit.ly/pe-sep21-mch]
1 12V DC plugpack, 1.5A+ [Altronics M8936D, Jaycar MP3486]
2 white (or black) insulated panel-mount RCA sockets
(CON6a,CON7a) [Altronics P0220, Jaycar PS0496]
2 red insulated panel-mount RCA sockets (CON6b,CON7b)
[Altronics P0218, Jaycar PS0495]
2 plastic TO-220 insulating bushes
2 M3 x 6mm panhead machine screws
1 M3 x 10mm panhead machine screw
2 M3 flat washers
3 M3 shakeproof washers
1 M3 hex nut
2 3mm inner diameter solder lugs
2 3mm inner diameter fibre washers
1 8mm tall adhesive rubber foot [Altronics H0930, Jaycar HP0825]
4 12mm round slim adhesive rubber feet [Altronics H0896]
1 1m length of heavy-duty figure-8 shielded audio cable
[Altronics W2995, Jaycar WB1506]
1 30cm length of 2.4-3mm diameter black or clear heatshrink tubing
1 30cm length of 5mm diameter black or clear heatshrink tubing
PCB assembly parts
1 double-sided PCB coded 01106201, 99.5 x 247.5mm
1 150µH 5A toroidal inductor (L1) [Altronics L6623]
2 47µH 0.5A bobbin-style inductors (L2,L4) [Altronics L6217]
1 100µH 5A toroidal inductor (L3) [Altronics L6622, Jaycar LF1270]
13 4-5mm ferrite suppression beads (FB1-FB13)
[Altronics L5250A, Jaycar LF1250]
2 M205 fuse clips (F1)
1 5A fast-blow M205 fuse (F1)
3 16x22mm TO-220 PCB-mount heatsinks (HS1-HS3)
[Altronics H0650, Jaycar HH8516]
1 PCB-mount DC barrel socket, 2.1mm ID (or to suit plugpack)
(CON1) [Altronics P0620, Jaycar PS0519]
2 tall 6x2-pin header sockets, 2.0mm pitch (CON2,CON3)
[Samtec ESQT-106-03-F-D-360; available from Mouser]
2 4-pin polarised headers with matching plugs, 2.54mm pitch
(CON4,CON5) [Altronics P5494+P5474+P5471, Jaycar HM3414+HM3404]
3 mica or rubber TO-220 insulating washers
3 plastic TO-220 insulating bushes
3 M3 x 6mm panhead machine screws
3 M3 flat washers
3 M3 shakeproof washers
3 M3 hex nuts
1 60 x 70mm rectangle of Presspahn, Elephantide or similar
insulating material
Semiconductors
1 CS5381-KZZ stereo 192kHz ADC, TSSOP-24 (IC1) [#]
7 NE5532AP or NE5532P dual low-noise op amps, DIP-8
(IC2-IC5,IC8,IC10,IC11)
2 CS8421-CZZ stereo audio sample rate converters, TSSOP-20
(IC6,IC7) [#]
1 CS4398-CZZ stereo 192kHz DAC, TSSOP-28 (IC9) [#]
1 MAX22345SAAP+ 4-channel high-speed digital isolator,
SSOP20 (IC12) [#]
1 DS1233A-10+ 3.3V supply supervisor, TO-92 (IC13) [#]
Audio Precision testing
The third measurement method we used was to hook the
SuperCodec up to an Audio Precision System Two (AP2)
analyser. This was mainly to verify that the above results
were all correct, and we weren’t somehow fooling ourselves
20
1 4N28 optocoupler, DIP-6 (OPTO1) [Altronics Z1645]
1 ACHL-25.000MHZ-EK 25MHz clock oscillator module (XO1) [#]
2 LM2575T-ADJG 1A buck regulators, TO-220-5 (REG1,REG2) [#]
3 LM317T 1A positive adjustable regulators, TO-220
(REG3,REG6,REG8) [Altronics Z0545, Jaycar ZV1615]
1 LM337T 1A negative adjustable regulator, TO-220 (REG4)
[Altronics Z0562, Jaycar ZV1620]
1 LP2950ACZ-3.3 100mA 3.3V low-dropout regulator, TO-92
(REG5) [Altronics Z1025]
1 AZ1117H-ADJ 1A adjustable low-dropout regulator, SOT-223
(REG7) [Altronics Y1880]
1 BC547 or BC549 100mA NPN transistor (Q1)
2 high-brightness 5mm LEDs (LED1,LED2)
9 1N4004 400V 1A diodes (D1,D22-D29)
2 1N5822 40V 3A schottky diodes (D2,D3)
12 BAT85 30V 200mA schottky diodes (D5-D16) [Altronics Z0044]
Capacitors
1 2200µF 25V low-ESR electrolytic [Altronics R6204, Jaycar RE6330]
1 2200µF 10V low-ESR electrolytic [Altronics R6238, Jaycar RE6306]
4 470µF 25V low-ESR electrolytic [Altronics R6164, Jaycar RE6326]
1 470µF 6.3V low-ESR organic polymer electrolytic
[Panasonic 6SEPC470MW] [#]
1 220µF 25V low-ESR electrolytic [Altronics R6144, Jaycar RE6324]
4 100µF 25V low-ESR electrolytic [Altronics R6124, Jaycar RE6322]
8 47µF 50V low-ESR electrolytic [Altronics R6107, Jaycar RE6344]
1 33µF 25V low-ESR electrolytic [Altronics R6084, Jaycar RE6095]
4 22µF 50V bipolar electrolytic [Altronics R6570A, Jaycar RY6816]
14 10µF 50V low-ESR electrolytic [Altronics R6067, Jaycar RE6075]
1 1µF 63V electrolytic [Altronics R4718, Jaycar RE6032]
2 1µF 25V X7R SMD ceramic, 2012/0805 size
[Vishay VJ0805Y105KXXTW1BC or VJ0805Y105KXXTW1BC] [#]
1 220nF 63V MKT
19 100nF 63V MKT
17 100nF 25V X7R SMD ceramic, 2012/0805 size
[Kemet C0805C104M3RACTU] [#]
4 22nF 63V MKT
7 10nF 63V MKT
9 10nF 50V X7R SMD ceramic, 2012/0805 size
[Kemet C0805C103J5RACTU] [#]
2 2.7nF 100V NP0/C0G SMD ceramic, 2012/0805 size
[TDK C2012C0G2A272J125AA] [#]
4 1.5nF 63V MKT
8 470pF 50V NP0/C0G ceramic [TDK FG28C0G1H471JNT00] [#]
1 220pF X7R SMD ceramic, 2012/0805 size [AVX 08052C221K4T2A] [#]
2 100pF NP0/C0G/SL ceramic [Altronics R2822, Jaycar RC5324]
2 33pF NP0/C0G ceramic [Altronics R2816, Jaycar RC5318]
Resistors (1/4W 1% metal film types)
5 47k 6 10k
2 5.6k 4 2.4k 2 1.5k
14 1.2k 3 1k
4 750 4 680 1 560
2 330 2 270 4 240 2 220 4 91
1 0 (or 0.7mm diameter tinned copper wire)
4 10
Resistors (1/10W 1% SMD types, 2012/0805 size) [#]
2 47k 5 2k
2 1k
1 220 1 22
1 10
All components marked with [#] are available from Mouser.
Jaycar/Altronics references are used to provide builders
outside Aus/NZ with enough information to source alternatives.
Likewise, there are lots of possibe vendor tips and ideas here:
https://www.siliconchip.com.au/Shop/6/5597
by using the Sound card to measure its own performance.
We ran three tests: one to test the DAC in isolation, one to
test the ADC in isolation, and one to test the whole system.
The first test involved feeding digital sinewaves to the
SuperCodec’s DAC, with its outputs then fed into the AP2’s
Practical Electronics | September | 2021
.01
SuperCodec ADC THD+N vs Frequency
19/05/20 14:51:30
.01
Total Harmonic Distortion (%)
Total Harmonic Distortion (%)
19/05/20 15:20:11
.005
.005
1V RMS (0dB)
0.5V RMS (-6dB)
.002
.001
.0005
No attenuator
8.0dB attenuator
.002
.001
.0005
.0002
.0002
.0001
SuperCodec loopback THD+N vs Freq.
20
50
100
200
500 1k
2k
Frequency (Hz)
5k
10k
20k
Fig.10: THD+N (not THD) at two different signal levels
Fig.10
for the SuperCodec’s ADC, using
our Audio Precision
System Two as the signal source. The rise in distortion with
increasing frequency seems to be an artefact of the way the
audioTester software calculates THD+N. We don’t think it
is a real effect. The true THD+N level for the ADC is well
below 0.001% across the whole frequency range.
distortion analyser. This yielded SNR
and THD+N measurements both of
106dB, and the distortion vs frequency
and level plot of Fig.9.
These figures match the expected
performance given in the CS4398
IC data sheet pretty much precisely,
suggesting we’ve built the circuit
correctly!
The second test involved feeding the
AP2’s low distortion sinewave generator into the SuperCodec’s ADC and plotting similar curves, shown in Fig.10.
These curves are a bit ‘wonky’ due
to the weird way that the software
we used (audioTester) calculates
THD+N, as we will explain in a
later article. But despite this, they
.0001
20
50
100
200
500 1k
2k
Frequency (Hz)
5k
10k
20k
Fig.11: THD+N (not THD) calculated in a loopback manner,
ie, using just the SuperCodec with its outputs feeding its
inputs. As the nominal DAC output level is 2.4V RMS and
the maximum input level is 1V RMS, its performance is
best with an 8dB resistive attenuator (1.5k/1k) between
the outputs and inputs. Otherwise, the SNR is degraded by
an additional 7dB or so.
confirm that the ADC performance
is just slightly worse than the DAC
performance, mainly to do with its
lower signal levels.
The final test involved running more
loopback tests, but this time using
the audioTester software to measure
THD+N, so that we can make a direct
comparison to the Audio Precision figures. These curves are shown in Fig.11.
This time, there appears to be an artificial drop at higher frequencies, which
we think can be ignored. Our assumed
real performance is pretty much flat, as
shown by the dashed lines.
So it seems that a measurement system based around a PC, the SuperCodec
and some low-cost software has perfor-
mance approaching that of our Audio
Precision System Two, which cost
many thousands when new. Even good
used AP2s are priced at four figures.
Plus, you gain additional functions and
features with this solution compared to
the AP2, such as THD-only measurements (rather than THD+N).
Next month
The USB SuperCodec circuit is fairly
complicated, so we don’t have enough
room to describe it in this article. We’ll
present all the circuit diagrams next
month, along with an in-depth description of how it all works. Then we’ll
describe how to build and test it in,
along with tips on how best to use it.
Reproduced by arrangement with
SILICON CHIP magazine 2021.
www.siliconchip.com.au
Our test setup. We initially built a version of this card without the asynchronous sample rate conversion (ASRC) components,
shown at right. The performance is pretty much identical but it’s less flexible, so we decided to stick with the ASRC version.
Practical Electronics | September | 2021
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