Articles, Reviews and Measurements of Audio Products

Kali Audio MV-BT Review (Balanced Bluetooth Receiver)

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This is a review and detailed measurements of the Kali Audio MV-BT (Mountain View) Bluetooth receiver with balanced output. It was kindly purchased new by a member and costs US $99 including Prime shipping on Amazon.

At first I was disappointed with the plastic case that it comes in:

Kali Mountain View review balanced Bluetooth receiver.jpg

That disappointment went away once I powered the unit and turned the rotary control and a soft blue light showed the level on the arc.

Likewise, the stout balanced connectors are a huge step up from RCA connectors:

Kali MV-BT review balanced Bluetooth receiver.jpg

The application is in pro/sound reinforcement scenarios where you want to feed input from a consumer Bluetooth device. For us, it would be a nice way to add balanced output without risk of ground loops due to an extra power supply and susceptibility of such with RCA unbalanced connections.

Amazon customers complained about noise level and this will be one of the things I will be testing.

Kali Audio MV-BT Measurements...

Amazing Budget Amplifier Find: AIYIMA A07 TPA3255 Video Review

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You all have probably seen the review of the AIYIMA A07 here but for YouTube audience, they asked for budget finds so I thought I do a video on that:

Text review:


Do you need AC Noise Filtering For Your Audio Devices?

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Short video on the fact that most audio gear already has noise and surge protection in them obviating the need to have them externally.

Amazon basics amplifier teardown:

Polk Atrium 4 Review (Outdoor Speaker)

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This is a review and detailed measurements of the Polk Atrium 4 speaker. It was kindly sent to me by a member and costs US $177 from Amazon including Prime shipping.

As the saying goes, you have seen one outdoor speaker, you have seen them all:

Polk Atrium 4 review outdoor speaker.jpg

I don't know if the owner had it outside or not but there are a few specs that seem to have lost their color or started to rust.

Binding posts point down so take that into account when deciding where to mount them relative to your wires:

Polk Atrium 4 review sealed outdoor speaker.jpg

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field")...

HifiBerry DAC2 HD Review (Rpi HAT)

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This is a review and detailed measurements of the HifiBerry DAC 2 HD. It was kindly sent to me by a member already assembled on a Raspberry Pi board. The DAC2 HD costs US $99 from company website.

Here is a shot of the full assembly:

HiFiBerry DAC2 HD Review Rpi HAT DAC.jpg

Let's zoom into it:

HiFiBerry DAC2 HD Review TI PCM1796 Rpi HAT DAC.jpg

As you see it is based on TI/BurBrown PCM1796 which seems to be a common DAC chip for these "HATS" (option boards for Rpi).

For testing, I streamed test files using my Roon player over Ethernet to it (hence streaming scenario). Test files have to be static in this situation so I can't show you any sweeps (e.g. IMD versus Level).

HifiBerry DAC2 HD Measurements
As usual we start with our dashboard of 1 kHz, streamed to the board at fixed/max volume:

HiFiBerry DAC2 HD Measurements Rpi HAT DAC.png

Performance is not great. It is what we would expect a few years ago:

Best Rpi DAC HAT Review 2021.png

Specifications from the company indicate far better performance but with a fine...

Audio Blind Tests and Listener Training (video)

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I see so many people claiming to have done blind tests in youtube videos recently without knowing what it means to perform one. Also, the topic of training comes up with many abusing the term. So I decided on a whim to create a video on it. It is rather long at 44 minutes but you can speed it up if you like. I like to use it as a reference in the future so I don't have to keep typing the same answers over and over again.

There is also a reference to an article I wrote a few years ago based on research published at AES on usability of long term listening in blind tests:

Please let me know what you think of these lecture heavy videos.

NHT C3 Speaker Review (Sample #2)

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Right after I post the review of the NHT C3 speaker, the owner noticed that there was a dent in the tweeter [EDIT: mid-range]:

You can see the dent at 7:00 O'clock position. The owner requested an exchange from Amazon and another sample arrived. The new sample is perfect in that regard. So there went another 3 hours of measurements and here are the results:

NHT C3 Measurements Speaker 2 Spinorama CEA-2034 Frequency Response.png

I have taken the on-axis response of the last sample in bold red, and overlaid it on top of our new spin data. As you see, the response is essentially identical other than some flattening of the peak above 10 kHz. That could be the difference in samples. Or, it could be me having the speaker pointed slightly differently. I don't have a fixture that locks each speaker into...

Square Wave Testing of Audio Products (Video Tutorial)

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The topic of using square waves to test audio products comes up quite frequently. Turns out that it is not a very useful signal for this application due to its nature and how our audio systems work. In this video I explain and demonstrate the signal processing behind square wave and reasons they can be problematic in audio measurements.

As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using:

Periodic Audio Rhodium DAC Review

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This is a review and detailed measurements of the Periodic Audio Rhodium DAC and headphone amplifier/adapter. It was kindly purchased new by a member and drop shipped to me. It costs US $99 but company has it on sale for US $49.

The Rhodium looks like any other USB-C phone dongle:

Periodic Audio Rhodium DAC Review Headphone Amplifier Adapter.jpg

It was plug and play on my Windows 10 PC and that is how I tested it.

Rhodium DAC Measurements
As usual, I test these dongles as DACs (with high impedance load) so that we can assess its performance without the headphone amplifier portion (even though it is still in the loop):
Periodic Audio Rhodium DAC Measurements.png

Ah, this is not very good. Third-harmonic is quite high at nearly -81 dB which dominates the SINAD to the same tune. Output voltage is only 1 volt which means it will not have much power to drive high impedance headphones either.

Jitter test showed nice, flat noise floor but some data dependent jitter (due to 250 Hz square wave in j-test signal)...

Amazon Basics 80 Watt Amplifier Teardown

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This is a follow up to the review of the Amazon Basics 80 Watt Class D amplifier. As promised, here is a quick teardown of the unit:

Amazon Basics 80W Teardown.jpg

I must say it is much cleaner construction and layout than I imagined. Wiring is nice and neat. Larger components are glued down. There is no manual re-work in sight.

Architecture is simple. The board on the left is a switching power supply which in addition to low voltages, produces + and - 32 volts for the amplifier output stage. Can't see the main silicon that performs the amplification but seems to be a "chip amp" mounted underneath to take advantage of the chassis for cooling. This is much smarter than desktop chip amps which just use a small vertical heatsink instead of using the chassis. In use, the bottom of the unit barely got warm where the chip amp is located.

Electrolytic capacitors...

Amazon Basics 80 Watt Class D Amp Review

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This is a review and detailed measurements of the AmazonBasics Class D 80 Watt/channel power amplifier. It was kindly purchased new by a member and drop shipped to me. On Amazon, it cost US $128 but the owner found it on "Woot" for just $70. They are sold out there though.

Not a half-bad enclosure especially for the price:

Amazon Basics 80W Class D Amplifier Review.jpg

It was so confusing to see dual languages on the front panel and the back:

Amazon Basics 80W Class D Amplifier RCA Review.jpg

I left the bass and treble controls as you see them there. For testing, I adjusted the gain to 29 dB which is my standard for testing.

Amazon Basics 80W Measurements
As usual, we feed the amplifier a 1 kHz tone with enough amplitude to produce 5 watts and see what we get:
Amazon Basics 80W Class D Amplifier Measurements.png

Well, this is not good. Distortion (third harmonic) is quite high at around 68 dB causing the SINAD to be pretty close to the bottom of all the amps we have tested:
Best class D amplifier review.png

Frequency response...

Introduction to Audio Science Review YouTube Channel

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Decided to do an intro video for the channel.

AudioQuest PowerQuest 3 Video Review (AC Filter/Surge Protector)

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This is a video review of a test I have already done on the AudioQuest PowerQuest 3 AC Filter and Surge Protector:

As a bonus, I also briefly cover the topic of surge protection devices and best way of deploying them. And a teaser about future testing of AC mains.

Dynaudio Emit M10 Review (bookshelf speaker)

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This is a review and detailed measurements of the Dynaudio Emit M10 bookshelf, 2-way ported speaker. It was kindly purchased by a member and drop shipped to me. The one I have is open-box sample. New, they cost US $800 and come in both white and black.

The enclosure is fine but I am not sure it is any better than cheaper speakers:

Dynaudio Emit 10 Review speaker.jpg

The speaker terminals felt a bit cheap to me as well:
Dynaudio Emit 10 Review bookshelf speaker.jpg

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in...

Audio Technica ATH-M50X Review (Closed Headphone)

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This is a review, detailed measurements and equalization for the Audio Technica ATH-M50X. It is on kind loan from a member and costs US $149 on Amazon including Prime shipping. There are an incredible 24,000 reviews on Amazon! It averages 4.5 stars

Nothing looks fancy here:
Audio Technica ATH-M50X Review closed headphone.jpg

The fit was more or less the same as other closed headphones in its class with cups a bit rubbing against my ears. The cable is removable:
Audio Technica ATH-M50X Review closed pad headphone.jpg

The sample I had was well used with some of the pad surface starting to disintegrate.

Note: The measurements you are about to see are preformed using standardized GRAS 45CA headphone measurement fixture. Headphone measurements require more interpretation than speaker tests and have more of a requirement for subjective testing as a result. In addition, comparison of measurements between...

Understanding Audio Dynamic Range / SNR (Part 1)

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Hello everyone. I am a bit under the weather today so didn't do any measurements but thought I do a video on dynamic range / signal to noise ratio and what it means at high level. In a future video I will dive much deeper into how much of it we need. So consider this the first installment.

As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using:

Understanding FFT in Audio Measurements

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FFTs are the fundamental to many measurements I show in my reviews. You can search for it online but I am not sure you will find any easy to understand explanation of it that applies to the way we use them in audio measurements. So I thought I do a walk-through using the Audio Precision of what it means, and how its parameters can drastically change what it displays.

As I asked the video, please let me know if you like these kinds of technical tutorials. To be sure they are not as much "fun" to watch as audio debunking ones. :) So like to know if you want to see more of them or not. And whether you could follow this one which is probably one of the most difficult concepts we have in audio measurements.

While I have not done a full text write up on this, the concept is included in my tutorial on digital audio measurements...

Do USB Cables Make an Audible Difference (Kimber Kable Review)?

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This is a video digest of a few of my past reviews and measurements of various USB cables. Some of it dates back to 2017 which most of you probably have not seen:

Text versions:
Kimber Kable USB cable review:

Difference between various generic USB cable:

As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using:

Flux FA-12 Review (headphone amplifier)

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This is a review and detailed measurements of the FLUX FA-12 balanced headphone amplifier. It was kindly sent in for testing by a member and costs US $749 from the company direct.

I must say, this is a luxurious and substantial enclosure for a headphone amp:
Flux FA-12 Review balanced headphone amplifier.jpg

Size wise, it is like an enclosure for a 50 watt linear amplifier. Speaking of which, this is a (discrete?) class A amplifier.

Operationally I found having the low gain in the middle a bit odd. Like to see Low, Med, High in sequence. Another oddity is that to use unbalanced 1/4 headphone jack, you have to use unbalanced input. Balanced input only routes to balanced output:
Flux FA-12 Review balanced R2R volume Control headphone amplifier.jpg

Volume control is implemented using R2R relay so channel matching should be perfect for those of you using sensitive IEMs.

I could not find any safety/regulatory marks on the unit itself. When mains power supply is included in an audio device, I like to see third-party certification for...

PS Audio Noise Harvester Video Review

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I had a lot of request from Youtube audience to do some videos on effectiveness of AC filters and such. So I did a video on a device I had tested in the past: the PS Audio Noise Harvester:

If you have read that review, there is probably not much new in the video but here it is anyway:

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