DJM ACTIV Audio Ethernet EMI Filter Review (Bonus!)

[amirm]

This is a review and detailed measurements of the DJM ACTIV Audio Ethernet EMI filter. It was sent to me by the company and costs US $1,950.

If there was an attempt to justify the price of a small component like this, DJM has done it. The unit feels super dense and solid and a nice shiny finish and writing which doesn't come across in the picture well. There is an ethernet port and external power supply feed on the left of the indicator LEDs. The power supply is a proper, Meanwell supply. On the right is the outbound Ethernet port. Operation was automatic and without any impact despite me connecting and disconnecting cables a number of times.

This is a proper company building this device, unlike many high-end audio tweaks seeing specifications and certification not only in the company website, but also back of the device (abbreviated here):

Here is the filter specs:

I wish a transfer function graph was provided as I can't quite tell where the filtering starts from, other than full 100 dB at 10 kHz. Alas, I don't have equipment to measure noise and interference on Ethernet filter either so can't provide plot it that. But I did find an indirect way to do so at the end of this review.

DJM ACTIV Audio Ethernet Filter Measurements
As frequent readers of ASR know, my main focus is to see if the output of an audio device changes as opposed to what goes in it. That is what we hear and what ultimately matters. To that end, I pulled out the yet to be reviewed Eversolo DMP-A8 streamer for this testing (full review to come shortly) for the measurements here. Naturally Ethernet connection was used to stream test signal to the A8 and balanced analog outputs measured. Here is the dashboard of DMP-A8 with volume reduced one notch and Ethernet connection without the EMI filter:

Superb performance as we expect from Eversolo. However, there are some noise and distortion spikes (well under audible threshold < -130 dB). Can some of this be from Ethernet link? Let's insert the AVTIV Audio filter in the path:

There is no difference other than run to run variations. Note that this doesn't mean noise was not filtered. But that the A8 is implemented well as to be isolated from Ethernet. What is there as far as spurious noise components is inherent in the DMP-A8, not from incoming noise on Ethernet.

To see if any ultrasonic noise is filtered, I ran 1 MHz FFT with and without EMI filter:

Again, we see noise components but they must be internal as there is no difference with and without filter. I also tested with J-test signal with similar outcome:

I then decided to just look at the spectrum of noise without streaming anything to DMP-A8:

Again, no difference.

For the final test, I decided to use my AC transformer that powers my headphone measurement gear. This has proven effective in other interference tests and did the job here:

We see that there is no difference at mains 60 Hz interference but as we go higher in frequency, we progressively see more attenuation. Keep in mind though that the the graph is massively magnified with the top of the graph at whopping -130 dB or 15 dB below threshold of hearing. So this noise would not be audible in either case. But we do see that filtering does exist.

Conclusions
I commend DJM Electronics for not only offering to send this filter, but insisting that I test it despite me cautioning them that I have not found any of these devices to make a difference that would be audible. Note that their company's core business is EMI filtering and is not focused on audio per se. On that front, this seems like a performant device. I think it would have good application in industrial domain. I have for example heard of CNC machines causing interference over Ethernet.

For audio, my tests on high performance streamers shows that the product is not needed. However if you are experience data errors on Ethernet due to special situation you might have, the DJM Electronic's ACTIV Audio Ethernet EMI filter may help deal with that.

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

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

 

[SoundsGood2Me]

Thanks Amirm!
You keep me coming back.

More Power Amps! We all love seeing muscle and DACs are settled science at this point.

 

[Jim Taylor]

I think you made a mistake in the price. Shouldn't it be $1,950.00?

Jim

 

[amirm]

Yes, thanks. Corrected.

 

[milosz]

Is this thing even intended to be an audio accessory? Maybe testing gigabit ethernet bit-error-rate in a high RF field would have been more appropriate than testing the performance of an audio devices hooked to it in a "normal" domestic RF environment. Have you ever measured RF field strengths in your lab?

There are environments where there are very high RF field strengths in which networked computer equipment is expected to operate without fail - i.e., TV and FM transmitter sites, particle accelerator labs, factories with industrial plasma-cutters / induction heating / lasers and even MRI suites. I think those are the intended use case for this thing, not a home living room audio setup unless you live next to a 300-kW TV transmitter.

 

[amirm]

Is this thing even intended to be an audio accessory?

 

[WalterW]

How to blow $2000 in the air...

 

[pablolie]

I honestly don't even know why valuable testing time is wasted on this kind of stuff, which is known utter BS to anyone with a remote peripheral inkling of basic networking tech. It does nothing beneficial. It can't. Digital transmission of audio has built-in recovery, and this kind of device will add absolutely zero additional recovery capabilities.

Honestly I am disappointed in the takeaways from the review. Ethernet benefits zero from whatever esoteric "EMI filtering" this does. The protocols take full care of it... and if they don't you have other things to worry about than "EMI filtering". If EMI is strong enough to introduce constant multi-bit errors into your stream over short distances... move out from wherever you live. Brain cancer and such should be bigger concerns.

 

[WalterW]

Thanks fro the rewiew. I think there is a typo, it reads "There is difference other than run to run variations." I guess there is missing the "no".

 

[Chrispy]

Makes me think that this supposedly legit company saw all the bs products that sell to audiophiles, they figured why not build something that is likely to be far more effective and see if we can't open a new market for ourselves? Wonder what made them think that was a good idea, tho.

 

[amirm]

Ethernet benefits zero from whatever esoteric "EMI filtering" this does. The protocols take full care of it...

Only if it is within the retry count of TCP. After that, connection is dropped. Frequent errors prior to that would reduce throughput. Granted, none of this is relevant to home networks but for general networking in a "hostile" environment, it may have value.

 

[Palladium]

This would have worked if Ethernet wasn't already electrically balanced and isolated at the bare minimum.

Is this thing even intended to be an audio accessory? Maybe testing gigabit ethernet bit-error-rate in a high RF field would have been more appropriate than testing the performance of an audio devices hooked to it in a "normal" domestic RF environment. Have you ever measured RF field strengths in your lab?

There are environments where there are very high RF field strengths in which networked computer equipment is expected to operate without fail - i.e., TV and FM transmitter sites, particle accelerator labs, factories with industrial plasma-cutters / induction heating / lasers and even MRI suites. I think those are the intended use case for this thing, not a home living room audio setup unless you live next to a 300-kW TV transmitter.

Again fiber that is completely immune to EMI isn't even expensive these days even in a home setting.

 

[Chrispy]

Only if it is within the retry count of TCP. After that, connection is dropped. Frequent errors prior to that would reduce throughput. Granted, none of this is relevant to home networks but for general networking in a "hostile" environment, it may have value.

Curious did they provide any information as to what situations particularly their gear would be effective/useful?

 

[pablolie]

Only if it is within the retry count of TCP. After that, connection is dropped. Frequent errors prior to that would reduce throughput. Granted, none of this is relevant to home networks but for general networking in a "hostile" environment, it may have value.

TCP defaults to smaller window size as a rule (unfortunately there are hacks out there). It will greatly reduce "goodput" but it takes a lot of keepalive misses to totally drop a connection. And if a connection is dropped, we will certainly notice it in an audio stream.
EMI situations do exist especially in transitory situations, but TCP is designed to deal with that. If EMI leads to a mayhem, I'd run away.

PS: I have worked in core internet networking for over 20 years... and have never encountered a major payload corruption that couldn't be attributed to a clear equipment failure (and those happen). The theoretically possible cosmic ray bit errors... I have never seen one in that time, although I have been told by very credible people they exist.

 

[amirm]

Makes me think that this supposedly legit company saw all the bs products that sell to audiophiles, they figured why not build something that is likely to be far more effective and see if we can't open a new market for ourselves? Wonder what made them think that was a good idea, tho.

Probably the dozens of such products in the market from filters to switches.

 

[Palladium]

TCP defaults to smaller window size as a rule (unfortunately there are hacks out there). It will greatly reduce "goodput" but it takes a lot of keepalive misses to totally drop a connection.

It wouldn't matter anyway since the audio data is still buffered and error checked at the app level.

 

[amirm]

TCP defaults to smaller window size as a rule (unfortunately there are hacks out there). It will greatly reduce "goodput" but it takes a lot of keepalive misses to totally drop a connection. And if a connection is dropped, we will certainly notice it in an audio stream.
EMI situations do exist especially in transitory situations, but TCP is designed to deal with that. If EMI leads to a mayhem, I'd run away.

If the CRC check at driver level fails, then the entire packet is gone. TCP will retransmit a few times and then the connection will drop. Meanwhile, the player may also run out of data to play, causing glitches and pauses.

 

[amirm]

It wouldn't matter anyway since the audio data is still buffered and error checked at the app level.

App level? I don't know of any app level error checking that operates over TCP/HTTP in a LAN. They rely on TCP for that.

There are UDP level applications that perform their own checking (e.g. NFS) but that is not what is used in home audio streaming.

 

[pablolie]

It wouldn't matter anyway since the audio data is still buffered and error checked at the app level.

Indeed true... and even HD audio is a trivial data rate these days.

Weird stuff DOES happen. But it is extreme. If EMI is that bad and causes major data disruption at a few Mbps... chances are a nuclear event nearby happened... listening to HD audio at home may not be a major priority in such an eventuality - unless that's how one wants to go (not a bad choice in my eyes btw).

 

[Chrispy]

Probably the dozens of such products in the market from filters to switches.

Yeah that part is fairly apparent. Curious what the rest of their thoughts/plan were, though. It's not expensive enough to compete with the high end stuff....