Articles, Reviews and Measurements of Audio Products (As an Amazon Associate I earn from qualifying purchases)

Behringer UMC-204HD Dac and Headphone Amplifier Review

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Previously I had reviewed and measured the Behringer UMC-204HD which retails for a paltry $79 with excellent results. See: https://www.audiosciencereview.com/...ds/budget-dac-review-behringer-umc204hd.1658/

Question was asked about its headphone performance. So I setup a quick test, driving both my Audio Precision analyzer with 300 ohms (not ideal but good enough) and a pair of Sony MDRV6 headphones for subjective testing. As a comparison, I also put next to it the Exasound E32 which retails for $3,500.

Subjective results/listening test
I played one of my audiophile tracks and listened using my Z-series HP laptop in-built headphone out. Sound was good although at max volume, not deafening. I then switched to the Behringer. I had to turn up the volume on it to mid-position to get it to be louder than my laptop output. There, it provided a slight improvement in fidelity.

I then turned up the volume further and the fidelity went to hell...

Inside Your High-Res Music: Sound Liaison high resolution music clips

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Hello everyone. Here is another episode in my look inside different high resolution samples. Here, I analyze the free samples from the great indie label, Sound Liaison which as 2L, are kind enough to provide these clips for us to use: https://www.soundliaison.com/all-categories/6-compare-formats
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In this look, I examine the DXD files at 352 Khz using another program, MusicScope:

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This allowed me to play the files even in DXD and dsd formats.


As before, lots of surprises in this analysis. Issues in both DXD and DSD formats (especially the latter).

Exasound E32 DAC Review and Measurements

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I have been reviewing a lot of low cost DACs recently. I wanted to have a high-performance DAC as a reference. My best DAC is in my audio system and pain in the neck to relocate back and forth. So I set out to find a DAC in $2000 range (my cost). Idea was to have a very low noise/low distortion DAC that would be revealing of any tweaks put in front of them.

After getting suggestions from the forum, I short-listed it to Benchmark and Exasound. Both of them provide measurements on their site which gave me confidence of good design. As it turns out, I reached out to Exasound and they immediately answered so I went with them. I asked for accommodation pricing on E32 DAC and I received a good discount. As a professional courtesy I don't want to say how much that is. Suffice it to say it is similar to dealer margin for high-end products. Should this have been a transaction with someone I know, the discount is usually 10 to 20% higher. Still, I thought it was a reasonable...

Rocky Mountain Audio Fest (RMAF) 2017 Day 3 (Sunday)

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The third-day was a rather short one for me since the show closes early. But also because I attended an amazing presentation by Avalon as you will see later. It capped a very nice show and a relaxing one. I hope the show was successful for the organizers and it continues.

Rocky Mountain Audio Fest (RMAF) 2017 Day 2

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Here is my coverage of Day 2 of 2017 Rocky Mountain Audio Fest. As this was a full day, there was a lot more to cover. Hope you find it enjoyable and possibly informative.

Rocky Mountain Audio Fest (RMAF) 2017 Day 1

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Hello you all. So the day 1 at the Rocky Mountain Audio Fest (RMAF) came to a close. It was a calm and "orderly" day with little to gripe about :). Being part of the press, I did not have to wait in this line where last year they could not find my badge. :)

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The line had died a few hours later.

The rooms had light to medium attendees. But when I asked a few companies what traffic they were seeing, they all said it was quite high and they were very satisfied with it seeing how it is not the weekend.

The weather outside is perfect with leaves starting to turn and super comfortable temps. But what the heck is going on here???
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Monday is the day I fly out! How do we go from 70s to 30s with snow and then back to near 70s???? It does not compute!

Had great number of conversations with industry folks. Unfortunately i can't share much of it with you all. :D

Overall, nice, relaxing and...

Henry Engineering Matchbox II USB DAC/ADC Review, Measurements & Tear Down

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The Henry Engineering Matchbox II was loaned to me by a member for measurements and hardware teardown/review. I am not sure how well known this DAC is. It is targeted toward television broadcast world. It unusually has both ADC and DAC plus professional AES/EBU output (balanced version of S/PDIF). In that regard, it appropriately only has balanced inputs and outputs.

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Retail price is fairly high for consumer market but appropriate for professional use at $479.

Specs are rather modest, stopping at just 48 Khz sampling and bit depth of 16 bits. Again, this is fine for video applications where 48 Khz sampling is standard and 16 bits sufficient.

Measurements
As always, my go-to measurement is 24-bit, 48 Khz J-test signal. I had not noticed that this device is limited to 16 bits when I did the testing so the 24-bit depth of the signal is lost on it. Indeed, that shows up in the measurements:

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The...

Battle of S/PDIF vs USB: which is better?

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I was recently asked about merits of S/PDIF versus USB for audio DACs. It has been said that S/PDIF was designed for audio whereas USB is a computer interface. And that makes USB noisier and less desirable interface.

I think most of you know my opinion on this. But just in case, I believe USB to be a superior and more "correct" interface for audio. Problem with S/PDIF is that it makes the source the "master," forcing the DAC to chase its timing. This means that if the source S/PDIF signal is not very clean, it can impact target DAC performance. Fortunately over the years S/PDIF interface has been perfected a lot and even in low cost implementation it can be excellent.

Still, there is no reason to have this antiquated architecture. Using asynchronous mode USB, the DAC can set the cadence using a high-performance clock and force the source, in this case a computer or streamer, to follow it.

Yes, there is some risk of noise here as USB is a much more complicated interface...

Musical Fidelity V-DAC II Measurement and Review

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This is a review of the Musical Fidelity V-DAC II including measurements. Member Ron Party was kind enough to l0an this to me. This is an older DAC, dating back to 2012 or so and retailed for $379. It comes with an external power supply which looks to be a linear one.

As usual, my first measurement is J-Test signal at 48 Khz sampling and 24 bits. Here is the outcome as compared to iFi iDSD which is a much newer DAC at similar price point:

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As we see there, the noise floor of Musical Fidelity V-DAC II is lower than iFi iDSD even though its output is higher (i.e. has a better signal to noise ratio). Just eyeballing it, it seems to have 5 to 6 db advantage over iFi.

Given the linear power supply, its output is free of mains related harmonics. So overall, a very nice showing here.

I have also shown the performance of V-DAC using both its USB input and S/PDIF. S/PDIF was generated from my USB port using an Audiophilleo USB to S/PDIF converters. As...

Sigma-Delta Digital Audio Converters (DAC)

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The previous thread on DAC fundamentals provided an overview of conventional (Nyquist) DACs. This thread will introduce oversampling and the delta-sigma architecture that dominates the DACs used in consumer audio gear today.

A few definitions:

Nyquist = fs/2 = 1/2 the sampling frequency. This is the highest frequency that a sampled system can correctly capture and reproduce. Any higher, and the frequency information is lost. Note that Nyquist applies to the highest frequency in the signal, so an audio system can reproduce a 20 kHz sine wave ( a single tone) but not a 20 kHz square wave (which has many higher harmonics). A system sampling at frequency fs, e.g. 40,000 cycles per second (40 kHz), can acquire up to (but not including) 20 kHz signals.

Oversampling refers to how much "extra" bandwidth, or sampling rate, we have relative to the Nyquist rate. For the...

Digital Audio Converters (DACs) Fundamentals

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Author: our resident expert, DonH50

The purpose of this thread is to provide a quick introduction to digital-to-analog converters (DACs), the magical things that turn digital bits into analog sound. Previous threads have discussed sampling theory, aliasing, and jitter. Now we’ll get down to the hardware and take a look at some basic DAC architectures.

The two criteria most often used to describe a DAC are its resolution (number of bits) and sampling rate (in samples per second, S/s, or perhaps thousands of them, kS/s). If we think about producing an analog output both of these are important. The resolution determines the dynamic range (in dB) of our DAC, and sampling speed determines how high a signal can be output. As discussed in those earlier threads, resolution sets an upper limit on signal-to-noise ratio (SNR) and spurious-free dynamic range (SFDR, the difference between the signal and highest spur). For an ideal (perfect) DAC, we can find:

SNR = 6.021N + 1.76 dB; and,
SFDR...

Digital Audio Jitter Fundamentals Part 2

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Author: our resident expert, DonH50

We left Digital Audio Jitter Fundamentals talking about digital signals. However, error correction and design margins mean jitter on the digital bit stream is rarely an issue for the bit rates used for A/V systems. (At 10 Gb/s and above, it is a bigger issue.) When jitter is brought up as an issue in the audio world, we are talking about jitter on the sampling clock. This can happen for all the reasons mentioned before, but once that clock is used to drive your DAC, the jitter goes right to your ears (OK, there are a few steps along the way, but you get the idea).

Clock recovery is a complicated subject beyond the scope of this thread. Let’s just say getting a very clean, low-jitter clock takes some effort. As a result, jitter can run pretty high (several ns or more) in many audio systems. Make it an A/V system with...

Units, Symbols, and Terms, Oh My!

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Author: our resident expert, DonH50

Units, Symbols, and Terms, Oh My!
I had intended this to be a short overview of basic terms. Didn't work out that way, sorry. At least it may help in defining some basic terms for people who have not seen them, or have seen them and never knew what they meant. More likely it will simply bore us all to tears. Oh, well! - Don

Before starting a discussion on sampling and such, I thought I should define some of the units, symbols, and terms most of us use but perhaps not everybody understands. I am paraphrasing many of these terms in an attempt to be clear and concise for the non-EE’s among us, not to be completely rigorous, so if you know better please bear with me…

I = current in Amperes (A). This tells how many electrons per second are flowing through a wire (let’s leave RF fields out of it for now).

R = resistance in ohms (Ω). This is the resistance to current flow and is...

Digital Audio Jitter Fundamentals

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Author, our resident expert DonH50

Jitter 101
Jitter is yet another one of those things not terribly hard to understand but with lots and lots of nuances and seemingly hidden details. To begin, let’s define some terms, starting with aperture time.

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Figure 1 shows a signal we want to sample. It moves fastest (has the highest slew rate) at the center crossing. Zooming in, the time it takes the signal to change by 1 least-significant bit (lsb) in amplitude is the aperture time (tap). If we sample anywhere within this time window, the output will be the same code (assuming the amplitude starts and ends on a threshold). If we fall outside the window, the next code lower or higher will be output. For a sine wave of amplitude A and frequency f, the maximum slew rate is 2*pi*f*A (the magnitude of the first derivative with respect to time). For an N-bit ADC or DAC and that same sine wave input, the aperture time is 1/[(2^N)*pi*f] (the...

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 https://www.audiosciencereview.com/...s/do-usb-audio-cables-make-a-difference.1887/), 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.
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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...
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