Articles, Reviews and Measurements of Audio Products

Composition of a Square Wave (important!)

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Author: our resident expert, DonH50 (above title mine :) )

Building a Square Wave
Since I used a square wave as an example in another thread, I realized that what is common knowledge for hairy-knuckled engineers such as I and high-brow scientists like some of the other folk here, may still be mysterious to many audiophiles. I thought it might be worth recreating a simple set of plots that shows how we can make a square wave from a bunch of simple sine waves, i.e. single frequency tones.

For starters, we must realize that any signal can be represented by an infinite sum of single tones of the right amplitude and phase. This is a fundamental principle upon which all signal processing is based. Problems arise, like in many areas of life, when reality hits the theory... In this case, it's impossible for a real system to have infinite frequency response, sampled or not, and of course getting all those tones' amplitudes and phases just right when we add them up is...
Digital (Audio) Aliasing
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Author: our resident expert, DonH50

Here's an attempt to explain aliasing -- the frequency folding that happens whenever you sample a signal. As was discussed in the Sampling 101 thread, whenever you sample a signal at a rate of X samples/sec (X S/s), the highest output signal is < X/2, the Nyquist rate. That is, when sampling at fs, any frequency equal to or greater than fs/2 will be aliased to fall with the frequency band from 0 to < fs/2.

For CD-rate sampling at 44.1 kS/s, we can convert a signal no higher than 22.05 kHz, or aliasing will occur. If the ADC has sufficient bandwidth, it can capture a signal higher than that, but it will be folded back (aliased) into that 0 - 22.05 kHz region. If the ADC is perfect, the amplitude and phase will be unchanged, but the frequency will be reflected about the Nyquist frequency, 22.05 kHz. A picture may help:

This picture shows a frequency (x) axis with the Nyquist frequency (fs/2), sampling...
Digital Audio Sampling 101
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Author: our resident expert, DonH50

Sampling is a very complex problem but the basics are not all that difficult to understand. We’re simply taking samples of things, audio signals in this case, at a particular rate and resolution (terms to be defined in context shortly). Let’s start with the Shannon Sampling Theory, the basis for digital audio:

“If a function of time f(t) contains no frequencies higher than W Hertz, it is completely determined by giving the value of the function at a series of points spaced 1/2W seconds apart.”

Claude Shannon was researching information theory and the most efficient ways to transmit and recover information. Harry Nyquist, a controls expert, refined the theorem and gave us the well-known Nyquist frequency limit: the maximum bandwidth that can be captured by sampling at frequency fs is fbw < fs/2.

A few comments on the sampling theorem:

  1. It applies to an infinite series of samples of infinite precision (i.e. “analog” samples, or...
Wavelength vs. Frequency
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Author: our resident expert, DonH50

Wavelength vs. Frequency
Nothing special in this one, just a simple plot. When discussing distances, whether related to room interaction, comb filter effects, room treatment or whatever, there is often the assumption that bass frequencies are "everywhere" while higher frequencies can be "directed" or are "more directional". The reason for this argument has to do with wavelength -- the length of the total sonic wave at a given frequency. Like waves in the ocean, there is a certain distance from peak to peak of audio signals, and that is their wavelength. It is related to frequency; higher frequencies have shorter wavelengths. The actual equation is w = vp / f where w is the wavelength (e.g. feet), vp the propagation velocity (about 1130 ft/s for sound in dry air at sea level), and f the frequency (Hz). Room modes or comb filter effects happen when sound waves bounce off walls or interact with other surfaces, or even arrive...

Speaker and driver design at KEF

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This video starts slow but then picks up steam and covers a lot of fundamental problems of designing speakers and how KEF solved them in their Uni-Q drivers.

Definitely worth a watch even if you are not interested in KEF speakers.

Measurement and Review of TotalDAC D1 USB Cable

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This is a measurement of Total DAC D1 USB cable and filter. Member dallasjustice loaned this to me last year and it has been waiting for the right setup for me to test it. Now that I have that (see, I figured it was time to measure this cable.

This is a normal looking USB cable going in and out of a metal box that is about 2 inches long and 1.5 inch wide and 1 inch deep.

The one I have is gray and has no markings whatsoever. But otherwise looks the same, sans the extra length of the one I have. I estimate it to be around 2 meters/6 feet which their web site says retails for 360 euros. ex-VAT. That is about $428 at today's exchange rate. So not cheap at all.

The setup is as with the other thread with Sonore microRendu as the source (networked) player and the DAC, Schiit Modi 2. Here is a comparison of against generic long USB cable...
Do USB Audio Cables Make A Difference?
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Aftermarket USB cables seem to be all the rage with people paying as much as $15,000 for a short run of it!!! Lots of subjective performance reports are out there but none back with any objective measurements that demonstrates any difference. On the other side of the fence many believe there isn't or can't be any difference in USB cables ("they are all digital"). I thought it would be good to add some data to the conversation.

For my testing, I used the Sonore microRendu as my source host. This is a networked audio renderer and comes with improved USB implementation. See my review and measureents of the 1.4 version here:

For DAC, I used our perennial favorite, the Schiit Modi 2 DAC. Of course I say that in jest as this is by far the worst DAC I have tested. It seems to be highly sensitive to power and USB conditions. I figured if there is one...
Review and Measurements of EMO EN-60KDS Ethernet Isolator
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This is a review measurement of an Ethernet isolator cable (passive) which is sold to medical industry. Ethernet is normally an isolated interface with transformers at both end. Addition of this is likely for high voltage surges and such.

I was loaned one of these to test. As you see, it is a simple, in-line cable:

The unit retails for $204 in US and about 153 euros.

Searching on CA forum, seems like folks advocate its use to get rid of leakage noise. So I used the Sonore microRendu networked audio adapter which seems to be pretty sensitive to AC mains leakage. To make sure it didn't contribute any, I used my lap supply to power the microRendu.

The Ethernet connection is from my local lab switch which in turn connects to another larger switch in basement equipment closet. The cable from switch is about 6 feet. The isolator was placed at the end of the cable and terminating into...
Hardware Review and Measurements of Sonore microRendu v1.4
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Last year I reviewed the original version of networked audio streamer, Sonore microRendu. Recently someone offered to loan me the newest version 1.4 to test and measure. So here are the results.

The Sonore microRendu is a super light, tiny aluminum box, requiring external power to operate. The device is too light to support the weight of the cables attached to it and runs super hot. I don't recall the original version running this warm. I can barely keep my hand on it for a few seconds.

The microRendu comes with support for Roon which is the way I tested it. For external power, I tested it with iFi iPower power supply ($50), UpTone LPS-1 and my Lab Power supply.

Roon recognized the device after a minute of so of being powered on and reliability was good.

So as a way to network a DAC and remotely using it from your computer or NAS device, it works fine.

Retail price is $650 which is quite high. You can easily buy a computer for the same price...
SOtM SMS-200 Networked Audio Player Hardware Teardown and Pictures
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This is a follow up to my review and measurements of SOtM SMS-200 Networked Audio Player:

Here, I am tearing down the box and showing the guts. Hope you enjoy :).

The unit is rather small but pretty heft. The shroud is a heavy gauge anodized aluminum which gives me no doubt about its ability to dissipate the necessary heat. After taking off the very tight torx screws, we are greated to this beautiful sight:

As you see, it is a two-board configuration. The small board on top is the switchmode DC to DC converter (more on this later). The base board holds the microprocessor (most likely ARM based) and all the necessary peripherals.

I am a sucker for white solder mask and hence my comment about beauty. It doesn't do anything electrically but after decades of seeing green ones, it is an emotional relief. :)

Zooming into the power board...
Vinnie Rossi Ultracapacitor Power Supply Review and Comparison to UpTone LPS-1
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Here is a measurement, teardown and review of Vinnie Rossi Ultracapacitor Power Supply. As I have explained before, this class of device aims to use a set of super capacitors as the storage reservoir to power an audio device. The idea is supposed to be to provide a mains isolated source of clean power for small audio devices and digital tweaks. This is implemented using dual capacitor banks, one of which is charging while the other powers the external device.


The unit is quite pricey in my book at $995.

The direct competitor to Vinnie Rossi Mini is the Uptone LPS-1. The Vinnie Rossi Mini includes a power supply internally while the LPS-1 does not. Uptone sells the UpTone with a switchmode power supply from MeanWell.

For this testing, I used my iFi iDAC2 USB Dac which retails for around $350. It is a popular DAC so I thought it would make a good test subject.

Since I was recently testing the Uptone...
UpTone LPS-1 Linear Power Supply Review and Measurements
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Recently I measured the performance of UpTone ISO Regen, a device whose purpose is to clean up the USB power and signal. Alas, as shown in that review,, the supplied MeanWell switchmode Power Supply managed to actually inject AC mains related noise which did not exist without ISO Regen.

The proprietor of UpTone, Alex Crespi while accepting the above issue, said that only 30% of their customers purchase the Iso Regen with the MeanWell Power supply. Many others apparently buy it with one of their other products, the Ultacap LPS-1.

Due to kindness of one of the owners of LPS-1, I have a unit on loan to evaluate.

The LPS-1 came without a power supply. Looking on their web site, they optionally sell the MeanWell with it. Fortunately that is the power supply I have...
Review and Measurements of Mytek Brooklyn DAC
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Hello everyone. Courtesy of a friend of the forum :), I am in possession of boatload of new hardware to measure/test. I am starting with the well regarded Mytek Brooklyn DAC measurements.

This is a $2,000 DAC with support for MQA and DSD, balanced output, and multiple inputs (Toslink, S/PDIF, AES/EBU). It even has an analog input!

The Mytek Brooklyn has a very nice OLED display, volume control, remote and headphone output. Unit is self powered with its own AC input/internal power supply. The box is the size of a paperback book, albeit in square format. It is heavy enough to feel solid and stay put.

Driver installation was a breeze and all worked the first time. For some reason I cannot get into any of the menus. The four buttons in the front that are supposed to do that, do nothing in my loaned input. Maybe there is a lock function some place.

As usual, I threw the 24-bit, 12 Khz...
Bargain DAC Review: S.M.S.L Mini DAC - Sanskritt 6th
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Went to clean up my work area and I find a box. Look inside it and it is another low cost DAC which I don't even remember ordering. :) I unbox it and find a nice little Chinese DAC called "S.M.S.L Mini DAC - Sanskritt 6th." Here is the Amazon link where I bought it ($107.99 including Prime shipping)

As you see, it is a very functional device with multiple inputs, USB, Coax and optical. It comes with an external power supply which puts out 9 volts at 1.3 amps. It is mandatory as it would not power up with just the USB connection. It is labeled by their own name and seems a step above from cheap junk USB adapters thrown in by many other DAC companies.

The brushed, anodized aluminum case is hefty and stays put even with cables tugging on it. A...
Budget DAC Review: behringer UMC204HD
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Regular readers of this forum know that we have been searching for an excellent performing DAC for under $100. So far we have not found it. All DACs tested underperformed my reference, the iFi iDAC2 ($350).

If you missed them, here is the review of Schiit Modi 2:

And Micca Origen+:

Next up is a product from professional world (i.e. designed for music recording/playback), the behringer UMC204HD. I paid a meager $79.99 for it, shipping included:

As you can see, this unit does everything but wash dishes. You have headphone amp, stereo input capture, multiple outputs, microphone phantom power, MIDI, etc., etc.

The unit itself seems quite stout and much more stable than the...
Budget DAC Review: Micca OriGen+ USB DAC
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This is a performance review and measurements of Micca OriGen+ USB DAC and headphone amplifier.

I purchased the unit through Amazon for $109 including (prime) shipping.

As you see, the box is somewhat odd looking compared to typical DACs. But overall build feel is very good. The device is pretty hefty and for this price range, it has good number of features.

The good news stops at hardware though. Installing the software drivers in Windows 10 anniversary edition is quite convoluted. The only process that works is in their FAQ rather than manual. I never did manage to get it installed on my laptop. Frustrated I had my son install it on my desktop machine and he managed to get it working. If you want a plug-and-play device or a simple setup that just installs, look elsewhere.

The unit oddly has three outputs. One large headphone jack...

Review and Measurements of Budget ($20) DACs

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This is the measurements and review of two budget DACs, the FiiO Taishan and Signstek Mini USB DAC:
1. FiiO Taishan


My reference for comparison is the iFi iDAC2 which retails for $349 or 17 times more money.

FiiO does not have USB input. To feed it audio I used the Coax output of iFi iDAC2. SIGNSTEK does have USB input so I used that as a complete system. It also has Coax input but I could not get it to work. Nor could I find a manual for it.....
Sonore MicroRendu Hardware Teardown and Review
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Some of you have seen my previous measurements of Sonore MicroRendu ( If you have not, this is a device that "remotes" your DAC by letting you use Ethernet networking to connect to a USB DAC. Outside of this functionality, many buy this for the presumed improvement in audio fidelity. My measurements did not show such improvement however. And to this date, no one has produced any that show otherwise.

For a part 2 of this project I thought I open the unit and show what is inside. The unit is inside of a small, cheezy aluminum case. Put aside any expectation of high-end fit and finish here. A couple of screws opens the one end and lets the guts slide out. What is inside is a main "I/O" board on which there is a daughter card that holds the main CPU that runs all the software.

Dealing with the CPU part, it is a typical all-in-one SoC (System on a Chip) on a PC...
Measurements of Sonore microRendu Streamer
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NOTE: this is an updated review of microRendu. Measurements were updated to use bitperfect path and max volume.


One of the latest trends in digital audio is to use a "streamer" device. This is something that sits between your music server on the home network, with then direct connection to the DAC. A lot of such devices have been built with Windows and Linux operating system on top of PC computer hardware. Sonore's microRendu is different in that it is built as an embedded, black box implementation.

This thread is about its measurements and not a full review. But briefly, this is a tiny device the size of a set of playing cards:

Both the packaging and aluminum enclosure scream "budget" equipment. So if you are getting this device as audiophile bling to impress your friends, this is not it.

The unit as mentioned, is a "bridge." It sits on the Ethernet network at one end and USB connection...

Entreq "signal grounding" Preliminary Measurements

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Here are measurements of the Entreq "signal grounding" box. If you don't know what that means, you are not alone :). It is a type of device where you connect it to the ground or negative terminal of your audio signals and it is supposed to improve the fidelity of the system. I was kindly given a loan unit of Entreq Olympus Minimus for this testing by the company founder, "PO."

The box arrived a few weeks ago but have been too busy to test it until now. From the outside, it is a nicely made wooden box with a single terminal out back:

The box is very heavy so clearly filled with something substantial. I was not allowed to open the box so my evaluation is limited to measuring it.

I had thought of measuring a lot of things but once I got to it, the reality set in. The box has only one wire going to it, not two. That is, there is no return path for any electrical signal. Think of trying to test a...
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