This is a review and detailed measurements of the miniDSP U-DAC8 multichannel USB audio DAC. It was kindly purchased and drop shipped to me by a member. The U-DAC8 came out a few years ago but still seems like a current device costing US $255 from the company direct.
The U-DAC8 embodies simplicity and fitment for function:
A USB port in for data and then in the rear, 8 channels of output:
And an external adapter double the size of a typical phone charger.
Wiring will be messy though with that USB connection in the front. Would have been nicer to have a slightly larger box and put the USB in the back.
The U-DAC8 was plug and play with Windows 10, exposing 8 concurrently channels. You could build a PC home theater or multi-channel source with it easily.
Most PCs come with 5.1 output so getting up to 8 channels out of U-DAC8 is a plus. As would be expected performance improvement.
DAC Audio Measurements
As usual, we start with a 1 kHz tone at full amplitude and see what we get out of the DAC:
OK, this is not good. Distortion products are way up there as is enough noise to give us a very low SINAD of 78. This puts the U-DAC together with the rest of the students that have gotten a failing grade from us:
The U-DAC8 uses AKM's AK4440 DAC chip. It does everything internally which the U-DAC provides from creating the required supplies to output buffers. Its specifications state a "THD" of 93 dB. We are 15 dB short of that at 78. miniDSP's own spec is 0.006% which translates into SINAD of 84. So whether we take my measurements or theirs, we are way short of the performance of the chip.
I tested the other channels and they produced identical output.
Dynamic range was decent:
Intermodulation distortion versus level was well below my reference DAC:
Linearity showing was not as embarrassing as I expected it to be:
Multitone test shows that as frequencies go up, non-linearities increase substantially resulting in more distortion products:
We will revisit this in a bit later. For now, let's look at jitter:
Noise level is very high as it is but then it rises around our main tone at 12 kHz. I re-ran this test (not shown) at lower frequency and it did that there too. We call this noise modulation although usually the entire noise floor lifts, not just around our main tone. Audibility of this is not as bad but still, something we don't want to see in a high quality implementation.
Real awful response was awaiting us in the form of THD+N versus frequency:
What on earth is this? Not only do we have fairly high levels of distortion/noise, it is also frequency dependent. To make sure this was not a measurement anomaly, I tested that trough around 700 Hz versus 1.5 kHz next to it:
Distortion is definitely higher at 1.5 kHz, demonstrating that the previous graph was correct.
Even DAC reconstruction filter response was disappointing with low attenuation out of band:
The right side should be down at -90 dB and lower.
Conclusions
What a shame. I walked into this review excited that we would have a clean and simple 8-channel DAC that could let us build our own Audio/Video Receiver in a PC. Performance though is quite disappointing. As a minimum we should have seen performance similar to the AKM DAC chip specs. Where the shortfall is, I can't say given the simple design here. As much as I hate the crapware that comes with PC/gaming sound cards, they have much better performance for much less money than the U-DAC8. I hope miniDSP goes back to the drawing board and builds a proper version of this DAC.
Needless to say, I cannot recommend the miniDSP U-DAC8.
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As always, questions, comments, corrections, etc. are welcome.
I threw a bone at one of the panthers and it hit him in the head. No, it was not the headless one. Seems like he needs glasses as he used to be able to grab it mid-air. I am still searching to find an optometrist that specializes in pink panthers. When I do, I need lots of money to pay for the visit and eventual contact lenses (can't imagine the panther walking around with glasses -- the rest of the panthers would tease the heck out of him). So I appreciate generous donations to cover the cost using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The U-DAC8 embodies simplicity and fitment for function:
A USB port in for data and then in the rear, 8 channels of output:
And an external adapter double the size of a typical phone charger.
Wiring will be messy though with that USB connection in the front. Would have been nicer to have a slightly larger box and put the USB in the back.
The U-DAC8 was plug and play with Windows 10, exposing 8 concurrently channels. You could build a PC home theater or multi-channel source with it easily.
Most PCs come with 5.1 output so getting up to 8 channels out of U-DAC8 is a plus. As would be expected performance improvement.
DAC Audio Measurements
As usual, we start with a 1 kHz tone at full amplitude and see what we get out of the DAC:
OK, this is not good. Distortion products are way up there as is enough noise to give us a very low SINAD of 78. This puts the U-DAC together with the rest of the students that have gotten a failing grade from us:
The U-DAC8 uses AKM's AK4440 DAC chip. It does everything internally which the U-DAC provides from creating the required supplies to output buffers. Its specifications state a "THD" of 93 dB. We are 15 dB short of that at 78. miniDSP's own spec is 0.006% which translates into SINAD of 84. So whether we take my measurements or theirs, we are way short of the performance of the chip.
I tested the other channels and they produced identical output.
Dynamic range was decent:
Intermodulation distortion versus level was well below my reference DAC:
Linearity showing was not as embarrassing as I expected it to be:
Multitone test shows that as frequencies go up, non-linearities increase substantially resulting in more distortion products:
We will revisit this in a bit later. For now, let's look at jitter:
Noise level is very high as it is but then it rises around our main tone at 12 kHz. I re-ran this test (not shown) at lower frequency and it did that there too. We call this noise modulation although usually the entire noise floor lifts, not just around our main tone. Audibility of this is not as bad but still, something we don't want to see in a high quality implementation.
Real awful response was awaiting us in the form of THD+N versus frequency:
What on earth is this? Not only do we have fairly high levels of distortion/noise, it is also frequency dependent. To make sure this was not a measurement anomaly, I tested that trough around 700 Hz versus 1.5 kHz next to it:
Distortion is definitely higher at 1.5 kHz, demonstrating that the previous graph was correct.
Even DAC reconstruction filter response was disappointing with low attenuation out of band:
The right side should be down at -90 dB and lower.
Conclusions
What a shame. I walked into this review excited that we would have a clean and simple 8-channel DAC that could let us build our own Audio/Video Receiver in a PC. Performance though is quite disappointing. As a minimum we should have seen performance similar to the AKM DAC chip specs. Where the shortfall is, I can't say given the simple design here. As much as I hate the crapware that comes with PC/gaming sound cards, they have much better performance for much less money than the U-DAC8. I hope miniDSP goes back to the drawing board and builds a proper version of this DAC.
Needless to say, I cannot recommend the miniDSP U-DAC8.
--------
As always, questions, comments, corrections, etc. are welcome.
I threw a bone at one of the panthers and it hit him in the head. No, it was not the headless one. Seems like he needs glasses as he used to be able to grab it mid-air. I am still searching to find an optometrist that specializes in pink panthers. When I do, I need lots of money to pay for the visit and eventual contact lenses (can't imagine the panther walking around with glasses -- the rest of the panthers would tease the heck out of him). So I appreciate generous donations to cover the cost using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
