Friday, 21 March 2014

MEASUREMENTS: Audioengine D3 USB DAC / Headphone Amp.


In the last couple of years, we have seen a proliferation of small sized USB DACs. Devices small enough for laptop-sized portability aimed at the headphone user who wants a bit more power to drive better 'cans' and provide improved sonics than what's available through the laptop's phono jack.

I guess it must have begun with the AudioQuest Dragonfly back in 2012. Currently in the 2nd incarnation as version 1.2. Version 1.0 got quite a positive review in Stereophile among other magazines which has helped propel this class of device into audiophile acceptability (if not some mainstream approval?). With the Kickstarter success of the Geek (Out) last year, these devices continued to gather press.

To create a device like this can be difficult given the dependence on the USB port for power. I've certainly experienced first hand the noise pollution from plugging my TEAC DAC into the computer USB port and this being picked up by my Emotiva XSP-1 preamp's analogue passthrough. That was why I bought the USB-to-ethernet cable extender to provide some noise isolation that thankfully worked.

So, a few weeks ago as I was perusing the local computer store, I ran into a sale on the Audioengine D3 USB DAC. I figure, what the heck - at less than $180CAD, it'll give me something to play with and if it sounds good, maybe it'll accompany me on overseas trips with a good pair of headphones.




I'm not new to the Audioengine brand. I've been using their A2 powered speakers on my desktop for at least 2 years now and can certainly vouch for the build quality. As you can see from the picture above, the D3 package comes with the DAC itself which has 2 LEDs - white for power, and a blue one that lights up with 88 & 96kHz audio. It also comes with a good quality phono adaptor for 6.3mm(1/4")-to-3.5mm conversion. There's also a functional grey fabric pouch for the DAC - useful to prevent it from scratching other things due to the "metal injection molded" aluminum case which makes the device feel quite solid in the hand.

I made it a point to take a picture of the text on the side of the box as well. As you can see, Audioengine likes to drop some hints on what's inside... The DAC is the AKM4396 (same as my Squeezebox Transporter), and the audio amplifier is the LME49726 opamp. The 2Vrms output level is good as standard line level RCA also. Asynchronous USB communication rounds out the specs. About the only concern I had was the 10-ohm output impedance on the device (see Tech Specs). This suggests that the DAC would best be suited for 80+ohm headphones (see here for details).


One of the things I always check with headphone outputs is whether it's loud enough with my AKG Q701 as pictured above (the Audioengine A2 speaker can be seen also). Happily, it does indeed power the Q701 reasonably well. I can listen to dynamic music without needing to push the volume to 100% which I'll speak more about later.  Also in that picture you see the 2 LEDs lit up. The inner one is power, the outer slightly bluer one is for >48kHz audio.

One observation is that because of the aluminum case, this little USB DAC can get pretty warm after awhile. Not enough to burn fingers of course, but mildly uncomfortable if you put it in a shirt pocket for example while on the go (cools down quickly though). Make sure to use the little supplied pouch!

One last thing before we get to some measurements. This little DAC does not require a driver in Windows or with the Mac (alas, I do not have a Linux machine handy). There's no ASIO driver for that TI1020B asynchronous USB chip inside and audio will be sent out based on the Windows Mixer settings by default. This is also how you control the volume. Remember that if you don't want Windows to resample, make sure to go in and manually change the sample rate settings in the "Sound" panel. As with most of these Windows driverless mini-DACs, the maximum samplerate is 24/96 and no DSD support (like the Dragonfly - I assume the Geek Out will require drivers for DSD and >24/96). IMO this is not a problem. More important than DSD and 24/192 for me is that it can handle 88kHz natively for my DSD-to-PCM conversions (which this does).

There is one other way to get a bit-perfect stream without ASIO in Windows - use WASAPI (Windows Vista onwards). The foobar WASAPI component worked well for me and I used that for all the measurements with the Windows machines. WASAPI will do the samplerate switch automatically with this device.

I. Objective Measurements:


A. The Basics
As usual, let's start with getting some charts and numbers out there for the product so we can get a sense of what we can expect from the sound.

First, the digital oscilloscope displaying the 0dBFS 1kHz square wave (connected to ASUS Taichi Ultrabook):

That's some nice looking square waves! (See Addendum 2 - the shape here looks better due to clipping.) Essentially no overshoot and no ringing. Remarkably precise channel balance which handily beats the ASUS Essence One. Gotta say that I'm quite impressed by this graph since this is "just" a small USB DAC. A healthy 2.83V peak (which would correlate to a 2Vrms sine wave).

Impulse response (16/44) off Asus Taichi Ultrabook:


Standard symmetrical linear phase filter used. Typical of sharp roll-off filters as seen in a previous post. Absolute polarity is maintained.

-90.3dB 16-bit & 24-bit Signal (off ASUS Taichi Ultrabook):
16-bits
24-bits
Have a look at the "Waveform Peeping" page for some comparisons. Better-than-90dB dynamic range resolution. Enough resolution to demonstrate the -90.3dB square waveforms created by flipping the least significant bit of a 16-bit signal. It's not as clean/precise as my full-fledged desktop DACs like the Essence One or TEAC UD-501. The waveform appearance is reminiscent of the Squeezebox Touch but better in that there's no DC shift and the channel balance even at such low amplitude is better. Again, not bad at all for USB power off a laptop/ultrabook.

B. RightMark 6.3.0 (newest free version now with ASIO capability)

UPDATE: See the latest update demonstrating clippling at 100% volume with this device! So long as you keep volume setting down a few clicks (~92% in Windows), the following test results apply.

So far so good. It's time to grab some RightMark results to see how it fares in terms of distortion, dynamic range, noise level, etc.

Since this is a portable device which is dependent on the computer for power, I think one of the most important questions to answer is how well it functions between different machines. So far, I have not seen any reports looking at the variability between machines in the objective tests with these small USB DACs. With that goal in mind, I'll be providing results with a number of different computers.

Setup:
Test machine + AudioEngine D3 --> shielded phono-to-RCA cable --> E-MU 0404USB --> shielded USB --> Win 7 laptop running RightMark 6.3.0

Summary of the machines tested (the laptops were described here in more detail although OS was updated in some cases):

1. ASUS Taichi 21 Ultrabook (early 2013): Intel "Ivy Bridge" i5-3317U (1.7GHz dual), 4GB, Windows 8.1 x64, 128GB mSATA SSD, USB3 port, foobar + WASAPI component

2. Apple MacBook Pro, 17" (early 2008): Intel Core 2 Duo (2.6GHz dual), 6GB, OS X 10.8.2 "Mountain Lion", USB2 port, 240GB SATA SSD, Decibel 1.2.11 player

3. Apple MacBook Pro, 15" (mid 2009): Intel Core 2 Duo (2.26GHz dual), 8GB, OS X 10.9.2 "Mavericks", USB2 port, WD 640GB SATA HD, iTunes 11.1.5 (AIFF files)

4. HTPC: Intel "Haswell" Pentium G3220 (3GHz underclocked to 2.5GHz & undervolted, dual core), 400W Seasonic fanless power supply, 8GB, Windows 8.1 x64, USB3 port, 240GB SATA SSD, foobar + WASAPI component

5. Server: AMD "Trinity" A10-5800K APU (3.8GHz quad), 700W Antec power supply, 16GB, Windows Server 2012 R2, 128GB SSD + bunch of HD's inside! USB3 port, foobar + WASAPI component

6. Workstation: Intel "Ivy Bridge" i7-3770K (3.5GHz quad), 800W Antec power supply, 16GB, Windows 8.1, 240GB SSD + 2 HD's. USB3 port, foobar + WASAPI or + JPlay 5.2B (newest 6/12/2013 trial, Kernel Streaming/ULTRAstream/DirectLink).

Except where stated with the MacBook 15", all the audio files were encoded in FLAC. The D3 was connected either directly to the laptop or the desktop machine's motherboard USB connector (ie. no hub in between).

For those unfamiliar with computer hardware, the above may seem too technical. I just want to make sure I covered the variables thoroughly. Let's just say that this is a pretty decent range of machines from laptops to desktops and the CPUs range from relatively slow by today's standards (Pentium G3220) all the way to a reasonably fast Intel i7. Macs are a bit older as I've transitioned away from Apple in the last few years for work. I focused on USB3 ports where available as the standard these days. I'll throw in both OS X "Mountain Lion" and "Mavericks", Windows Server 2012 R2, as well as the JPlay software in one of the tests using the most extreme settings.

16/44:
Summary of this USB DAC connected to each computer:

Frequency Response

Noise Level
THD
IMD
As expected, these days, any advertised high-resolution DAC should have absolutely no issue with standard resolution 16/44 signals. We're basically looking at ideal and identical results here with this little USB dongle on all the computer hardware platforms. Clearly, from the frequency response, the AKM4396's standard "fast roll-off" filter is being used instead of the "slow roll-off" option for the chip (you can see the effect here with the Transporter).

24/96:
Now we move to high-resolution:


From the numbers it's looking really good across the board. No surprises with any of the machines and minimal inter-test variability.

Frequency Response

Noise Level

THD

IMD
Notice the use of JPlay for one of the measurements with the i7 Workstation setup. As with previous testing, there's no evidence of difference even with what I believe are very high settings - ULTRAstream / DirectLink. Also the MacBook Pro 15" used iTunes and AIFF uncompressed files rather than the standard FLAC with the others - again, no difference.

Here's the stereo crosstalk graph. Remember that this is highly dependent on the analogue interconnect cable used so doesn't really say much about the DAC per se. In this case, I'm using a short 3' length.



C. Jitter
Okay, to finish off, let's see if the J-Test shows any significant sidebands.







Some minor variation in noise between the machines (some of which I'm sure contributed by the E-MU 0404USB) but it's all rather low level and of no concern. Jitter modulation pattern easily visible in the 16-bit test. As usual, these J-Test graphs are meant for analysis of SPDIF interfaces. Asynchronous USB converters almost universally do not demonstrate issues. As I have said before, I doubt jitter is audible these days given how good even basic DACs are in this respect. I would seriously like to see evidence to suggest a need for stuff like "femto clocks" suggesting any difference that would be audible!

II. Comparisons:

One of the fun things about using the same test kit over the last while is that I've got a little database of objective results to make relative comparisons. Here's how the D3 stands compared to my other units (24/96 only, there's no point comparing 16/44):


The first 2 columns are the Audioengine D3 playing off my ASUS Taichi Ultrabook either on AC power or unplugged with the battery. Notice there is no difference. Some folks feel that running off battery power results in less noise; I certainly did not see that here.

A reminder - the better stereo crosstalk values for the D3 are because of shorter analogue interconnect cable (3' vs. 6').

look at the graphs:
Frequency Response

Noise Level

THD

IMD

As you can see, the outlier here is the Squeezebox Touch with the "poorest" performance (realize though that the performance is still excellent!). The SB Touch rolls off the bass a little earlier than the others (-1dB by 20Hz) and with the highest noise level.

Although buried in the various overlaid graphs, the D3 noise level is remarkably low around 60Hz (mains fundamental frequency).

The Audioengine D3 fits at an intermediate level between the SB Touch and the rest of the high-performance DACs. The noise level is just a hair above the larger full-sized DACs. There's also more ultrasonic roll-off which I believe is inconsequential.


III. Subjective Evaluation:

I spent about 2 weeks listening with this headphone amp / DAC combination in the evenings while doing some other work. It sounds very good. Headphones used in the evaluation include my JVC HA-FXC51B IEM, Sony MDR-V6, AKG Q701, and Sennheiser HD800. With an output impedance of 10-ohms off the Audioengine D3, it's recommended to have >80-ohm headphones to maintain a relatively flat frequency response. Of the group, the worse impedance match would be the JVC IEM at 16-ohms. Despite this, the sound was quite nice if a bit bass shy with an accentuated mid-range that worked OK for some pop and rock recordings I was listening to (Donald Fagen's The Nightfly, Cat Stevens Tea For The Tillerman). I took the ultrabook, D3 DAC, and these IEMs around one weekend while my son was doing his sports lessons and it did not seem too cumbersome.

The sound was good with the 63-ohm Sony V6. These 'phones have plenty of bass and I had a chance to listen to a few vinyl rips. For example on Falco's Rock Me Amadeus (1985 Canadian Release) vinyl rip, you can hear the limitations of the digital sampling used in those days with an elevated background noise during the vocal overlay in the 1st half of the song. Daft Punk's Random Access Memories vinyl rip sounds very good as well with some surface noise reduction.

As I mentioned above, this little headphone amp can power the 63-ohm AKG Q701's reasonably well but I do push them up to ~80% with softer well recorded albums. For example, Rachel Podger's Guardian Angel (Channel Classics 24/96) sounds fantastic through these headphones. The open design of the AKG's are great for classical music transparency. I also find them very comfortable for longer listening sessions. Timbre and resonance of the violin in the recording space were well rendered... Enough resolution to easily hear the performer's occasional toe tap and breath sounds :-). As a side note, I do not recommend downloading the 24/192 versions off Channel Classics since the material was sourced from DSD64 and converted with Weiss Sararon - there's a steep lowpass filter in place and there's no audio above ~40kHz so 24/96 is more than enough. I also listened to the large choral arrangement of Mahler's Symphony No.8 ("Symphony of a Thousand") (Antoni Wit & Warsaw Philharmonic Orchestra, 2011 Blu-Ray rip). Comfortable listening level for this louder album was at ~65%. Lovely conveyance of the intermix of solo and choral voices; tons of detail to be unearthed in this recent Naxos recording of the 8th. [BTW, the multichannel mix is excellent as well!]

I spent a couple nights listening to the Sennheiser HD800 with this DAC. These are 300-ohm headphones so should be good impedance-wise and due to its sensitivity, can be driven to an uncomfortably loud volume (for me anyway). The thing I appreciate about the HD800 is that they're good at pretty much anything! The bass is tight without accentuation and the highs sound clean and dynamic. I keep wanting to use the term "precise" about the HD800. They can be very unforgiving of poor recordings; especially those with accentuated trebles (it's worth trying out the "Anaxilus mod"). First up was some Guns N' Roses - Appetite For Destruction (1997 MFSL release). Very good definition and detail even with loud and "busy" tracks like "Welcome To The Jungle". Not exactly high-fidelity but can still be used to judge quality of reproduction especially in teasing out the individual parts and making sure the sound doesn't become "muddy". Moving on to another memory of the 1980's, INXS' Kick (2002 Rhino remaster) sounded very good as well... I've always enjoyed the intro to "Devil Inside" with the synth-percussion and electric guitar as we get into Michael Hutchence's moderately reverbed vocals in this "classic" INXS lineup at their peak.

Moving on to the audiophile female vocalist genre... About 13 years ago, I was in Chengdu, China for some travelling when I came across a copy of Cai Qin's (蔡琴) "Golden Voice" (金片子 壹) album. This is one of the best recordings I have heard. If all CD's were recorded like this, I don't know who would even consider the need for "high-resolution". Needless to say, the rendition out through the Audioengine D3 and Sennheiser HD800 was fantastic. Simple instrumentation with the voice beautifully detailed consisting of classic Chinese songs originally written back in the early half of the 20th Century. I suspect many audiophiles would call this DAC/headphone combination "analytical". I just call it brutally honest; what I personally look for in true high-fidelity.

Finally, I hooked this little DAC using phono-to-RCA plugs to the Audioengine A2 powered speakers in the picture above to have a listen... My daughter really wanted to hear the Frozen soundtrack. Yup, sounds good - all that Disney high production value. Alas, although I really enjoy Idina Menzel's "Let It Go", I can never shake off the vision of Elphaba in my head! Overall, it sounds as good as my usual desktop DAC (ASUS Essence One) connected to the Audioengine A2 in terms of resolution and soundstage (within the limits of these small desktop speakers of course). So far I have not hooked this up to my main sound system downstairs (inconvenient re-routing of analogue cables). I suspect it will sound very good as well.

IV. Conclusions:

1. I was pleasantly surprised by the objective measurements! For something this small, the measured results are almost as good as the better DACs I've measured. All this driven off a USB port. Impressive.

2. Great to see that a USB DAC is capable of essentially identical performance off a number of different computer setups. The machines are of various age, make (Intel and AMD), both USB2 and USB3 ports used. Despite all the hoopla around fears of poor power quality or potential of electrical noise, this little device has demonstrated to me that these fears are unnecessary - or at least can be dealt with. It sounds clean, the noise floor is excellent. No evidence of jitter issues with the asynchronous USB interface.

3. Following from item 2, although previously demonstrated, again in these tests there were no significant differences in the sonic output with this DAC between computers running different OSes (Windows 8.1, Server 2012 R2, OS X "Mountain Lion", "Mavericks"), and playback software (foobar, JPlay, iTunes, Decibel). Likewise, I remain unconvinced that jitter is affected by anything other than the hardware interface itself. A good DAC and bit perfect is all that is necessary for quality playback as far as I can tell these days.

4. Specifically regarding the Audioengine D3, remember to keep the fabric pouch handy so as to avoid scratching other things packed with this stick due to the aluminum construction and sharp angles. Also, it does get warm after awhile. However, on the plus side, the construction is very solid! It might not have the color-changing Dragonfly, but the little blue LED is good enough to know when sampling rates have gone >48kHz. At 2.5" long (slightly longer than the Dragonfly), it does stick out from the computer a little bit but is generally unobtrusive.

5. Yes. Subjectively, the Audioengine D3 sounds very good and has enough power to drive my AKG Q701 - this is better than my TEAC UD-501. Most of my subjective headphone listening was done with the ASUS Taichi Ultrabook and desktop i7 workstation. I did not notice any difference in sound despite the different underlying computer hardware.

I think the proliferation of small high performance USB DAC / headphone amps is a good thing. I appreciate the recent Tom's Hardware article on computer audio suggesting that there's generally no need for anything better than the ubiquitous sound chip in the computer. That's probably also true. There's generally no need for better sound especially on-the-go where the ambient noise is high. However, "native" sonic capabilities of laptops can vary as I previously demonstrated. What a small device like this brings to the table are more power for demanding headphones and uniformly good sound quality off the USB port for whatever computer one owns. When I'm on the road with a good pair of headphones, this device will do nicely for listening in the quiet evening in a hotel...

Time will tell whether mini USB DACs like these will maintain much popularity however. For audiophiles it's not all that inconvenient to carry or plug in, but I'm not sure if this would continue to capture the interest of the mainstream market (assuming the interest in devices like the Dragonfly and Geek Out represents mainstream acceptance). In time, it's possible that laptops will on average achieve better sound quality which would negate the need for this class of device. We've already seen quality improvement with support of high sample rates and 24-bits. Remember the days of noisy audio where you can hear the electrical interference from spinning disk drives or busy CPUs? Or when everything was resampled to 48kHz? Thank goodness standards have improved.

I hope this review provides a good glimpse into how the Audioengine D3 measures and sounds. Certainly it has given me some perspective into this class of device as new ones come out. I 'hear' that the Geek Out is shipping in small quantities. I like that it has 2 outputs (one with <1-ohm impedance) and can deliver more power. Excitement is certainly there and things can get a little silly when this happens (as witnessed by this hilarious video). For the more powerful 1W model, I wonder what heat production and battery drain will be like with portable devices (supposedly Class A?). I'm most curious about how the crossfeed algorithm sounds. To date I have not found a headphone crossfeed DSP I've ever really liked. To call the feature "Awesomifier" I think could lead to the butt of many jokes if it actually doesn't end up "awesomifying" anything. Also, I saw on a video that it runs in non-oversampling mode which is certainly possible given the use of the PCM1795 DAC like I showed in these TEAC UD-501 measurements. I don't know if running this DAC in NOS mode (digital filters off) is wise for something like this. We should be seeing some reviews soon I hope...

OK, enough audio geekiness for now! It's Spring Break for the kids. Time for family R&R in the week ahead. :-)

Enjoy the tunes dear readers...

Addendum:
Around Christmas time I wrote a little opinion piece on the next gen video game machines and how I decided to just stick with the PC. Looks like indeed some of the new multiplatform games are probably best played on good ol' Windows... Wasted a few hours on this over the last few days :-)

Big push for Titanfall on the XBOX One but I think it's pretty clear that the Windows version has better visuals (true 1080P), better frame rates, and excellent gameplay even on a modestly powered machine.

Addendum 2:
Frans,
Managed to whip out the oscilloscope for a quick look...
-3dBFS 1kHz square wave, 44kHz
Slight Gibbs undershoot and overshoot seen, so clipping indeed likely contributing to the idealized appearance of the 0dBFS plot above. Nonetheless, still looks really clean and balanced compared to others...

15 comments:

  1. Good post, Archimago! I'm with you on the proliferation of these devices being a good thing. Lets you get good sound whether it's from a work computer, home desktop, netbook, whatever. Plus there is the option of connecting to smartphones and tablets with things like Apple's Camera Connection Kit. Lastly, a tactile interface can sure be nice sometimes.
    I backed the Geek Out (and the Pulse) and hope to have mine sometime in the next couple of weeks. They posted some updated measurements that show it whoopin' similar products, though the D3 is not listed. Time will tell.
    http://geek.lhlabs.com/force/geekout/898-geek-out-vs-the-others-3rd-installment

    ReplyDelete
    Replies
    1. Some follow-up: Just got my shipping notification for the Geek Out! Yeehaw.
      Second: the only crossfeed I've really messed with is the JRiver "headphones" setting. I've come to really enjoy it on the "Standard" setting. Total life-saver on older recordings with hard pans and gets rid of the artificially large soundstage. Most stuff has really been mixed to be played over loudspeakers. I'll try out the Geek Out one since it should let me use crossfeed on Spotify, Soundcloud, Youtube, VLC etc. but JRiver does a really good job when it comes to listening to files.

      Delete
    2. Thanks for the note Simon!

      Congrats on getting the Geek Out soon. Let me know what you think... Haven't seen any reports yet from end users. I'll give the JRiver crossfeed a try tonight. I've so far played with some foobar ones and VST plugins a few years back.

      Have a great weekend.

      Delete
    3. Thanks, you too! I'll warn you, crossfeed can make it feel like there is less separation and thus less detail or "accuracy" but it ends up being wayyyy less fatiguing for me. The first 30 or 60 minutes might be kinda weird. Try using it for a few days and see if you don't forget that it's there.

      Delete
    4. Thanks for the Geek measurements link, Simon.

      While I can't speak for the devices since I've never tried them, I think there's something wrong with the Dragonfly measurements... Looks like they're clipping it with THD+N up at >5%! Don't know if this is what happens to the Dragonfly at 100% volume or an issue with the measurements they did. Likewise, that 5kHz square wave looks odd.

      The iFi iDSD also doesn't look impressive at all if the measurements are correct. I'd be quite happy with the Meridian results though.

      Thanks for the note on crossfeed... I'll make sure to whip out some hard panned Beatles and see how it sounds.

      ----
      Addendum: I read the post a little more and indeed they're claiming the Dragonfly clips at 100% (0dBFS). Yuck. That's just poor... And they're claiming both versions 1.0 and 1.2 are like that.

      Delete
  2. I know this is a bit off topic, but what is the headphone output impedance of the Xonar Essence One?

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  3. What does the squarewave look like when it is at -3dBFS ?
    It seems to me the squarewave is exemplary simply because it is clipping.

    ReplyDelete
    Replies
    1. Interesting thought. Let me have a look at that in the next couple days...

      Delete
    2. It still looks surprisingly nice though with minimal overshoot (has 'impressed' look on face).
      Should I ever want to listen to well reproduced square-waves (and not use a NOS DAC) this would be a good candidate to do such with.
      There are no square-waves present in music signals though.

      What is kind of odd is that 2.83Vp and 2.42Vp has a distance of 1.36dB instead of 3dB.

      It makes me wonder about the behaviour just below 0dB output voltages.
      How does a 1kHz 0dB sinewave look like when zoomed in at the top (or bottom), does it show flattening or increased distortion ?
      I bet such clipping would be quite audible though and perhaps be dependent on the power supply voltage coming from the USB as well.

      Delete
    3. Thanks again Frans,
      I'll have a look at the sine wave later... I was pondering the voltage drop as well last night. Clipping near the 0dBFS level certainly could be audible for the frequently encountered loud pop / rock songs out there when played loud.

      When I did the tests, I did have to attenuate the volume a small amount because the E-MU was registering some "red lining". In retrospect I wonder whether it's not the E-MU at all since the peak voltage was not that high, but rather a situation like the Dragonfly measurements in Stereophile where the last few clicks up top was clipping...

      Thanks for the feedback, this really helps; I'll have a good look later tonight! I should have paid more attention to this!

      Delete
  4. Suggestion for Jitter Measurement

    Hi Archimago. As I mentioned in a reply in a former blog, that I enjoy reading your posts, to give a different sight of view, on some technical aspects.

    If you like, you may have a look at the software HpW-Works. This is for me for making home brew Jitter measurements the best software to do this.

    http://www.hpw-works.com/index.php/gallery/rme-bayface-gallery

    These measurements do correlate very well with that of the Audio Precision measurement system. You should give it a try. It is worth.

    Best Regards
    Juergen

    ReplyDelete
    Replies
    1. Thanks Juergen,
      I'll have a look!

      Delete