This is a review and detailed measurements of the Universal Audio Apollo X16 Interface (ADC, DAC and DSP). It was kindly sent to me by the company for testing and costs US $3,499. The X16 is the longest requested interface for us to measure going back to when I had barely started measuring audio electronics. Interest was driven by seemingly impossible distortion and noise specifications. So it is very fortuitous that we finally get to test it.
The X16 is designed for rack mounting:
The only computer interface is Thunderbolt ()TB). It was hell getting TB capability on my PC motherboard. Once there, I had to buy a cable which at $40 (from Apple) for a 2.5 foot version, was outrageous. Then again the interface is running at ultra high-speed with very low latency so the passive cables are short by definition. This made it hard for me to see the display on the unit so I have no feedback on it. However, I did use the extensive software package/control that came with the unit, to the tune of 600 megabytes!
As the name indicates, you have 16 channels in and out:
DB-25 connectors are used so if you don't have such break out "snakes," you need to buy them as I did. They are commonly available. Just make sure the mating is correct. Mine was a no name $50 one for the ADC portion which worked fine. For the DAC functionality I used the additional monitor out so didn't need to buy that snake.
As you see, a hefty external power supply is used, reminding me of the original Xbox power supply. Not that you would want to mess with replacing it but note that it mates with a 4 pin, XLR like DC connector to the unit.
I ran into a major stumbling block in testing the X16 in that it only exposes an Audio interface for 64 bit applications. The Audio Precision software is 32 bits so would not see it at all. My Roon player did as did Adobe Audition. If you are going to use this for hi-fi applications, be sure your app is 64 bits. My solution to testing was using the AES input on the X16 for most of the measurements. I provide a dashboard readout using Thunderbolt by playing the test tone using Roon player.
This review is focused on electronic performance of the X16. There is tons and tons of functionality in the X16 that I won't touch on, nor am I qualified to do so. Please seek out other reviews for that functionality which is likely responsible for good bit of cost of this unit.
Lots of programming capability exists to set up the unit. Per recommendation from UA, I set the unit to 24 dBu output. The default is 20 dBu, with the extra voltage left for headroom. Fortunately performance is just as good at 20 dBu.
FYI I reviewed the measurements with UA and they are fine with the results.
Apollo X16 Measurements: DAC
Let's start with our usual dashboard pushing bits using Thunderbolt:
Note that I have heavily reduced the output level to our standard 4 volt output. We get stellar distortion rating of -135 dBFS (20 dB below threshold of hearing). Being designed for higher output voltage, the SINAD which includes noise and distortion, is excellent but slightly below the best we can get on our desktop DACs:
If we untie the wings from the X16 however to push higher output level, it reaches the same heights:
SINAD is now clocking at 120 dB. Note that this is driven by the sum of the Audio Precision analyzer noise and X16. If you subtract the former, you get close to what the company has specified (123 dB THD+N).
Performance is same for AES/EBU digital input:
I ran into another common bug in Audio Precision software in that it has some kind of buffer underrun which drops bits. This causes the measurements to get corrupted. To avoid this, I had to turn off averaging to get a single snapshot so ignore the more busy noise floor of the FFT. As you see, performance is identical so we will use AES from here on.
Here is our dynamic range:
Company spec is 127 dB but it is with a-weighting.
Distortion is kept to a minimum especially in low frequencies where there is usually a rise:
Intermodulation distortion vs level naturally varies a bit depending on the output voltage:
Linearity is absolutely nailed:
Filter response is typical but with excellent attenuation:
As you see, the bottom fell out of the graph!
Jitter and spurious tones are of course kept under control regardless of input type:
Finally, a very clean THD+N versus frequency despite its much wider 90 kHz bandwidth:
Apollo X16 Measurements: ADC
For the target market, analog conversion is everything so let's see our dashboard there:
This places the X16 high on the ladder but not the top:
Sweeping the input level shows that this is about the best we can get:
Notice the very low noise level (SINAD above is dominated by distortion). You can see this in better dynamic range than SINAD:
Here is a drill down of a 1 kHz tone relative to RME ADI-2 Pro (non-FS version):
As you see, it is the third harmonic which holds the X16 back (in red). On others it tends to be lower.
At lower than max input, the X16 competes at the top of the class:
I had no luck trying to get the ADC to operate at higher sample rates even though I changed it to higher values. Likely an operator error. So this test of frequency response is not that meaningful:
Finally, here is our THD+N versus frequency:
The much better results once again indicates a clean response above the audio band.
Conclusions
It would have been a watershed event if we had tested the X16 when it came out as it would left all of our high-fi DACs in the dust. In the interim period those companies razor focused on best measured performance and given us incredible performance. Still, the X16 if left to produce its high output, is able to keep up with them and of course provide incredible amount of additional functionality to say nothing of 16 channels input and output.
The high output of X16 should allow you to drive amplifiers such as Purifi and Hypex without their input buffers and get better measured performance than you can with high-fi DACs. But do keep in mind the complexity of using Thunderbolt for interface/programming and need for 64-bit player application.
It is my pleasure to put the Universal Audio Apollo X16 on my recommended list.
------------
As always, questions, comments, recommendations, etc. are welcome.
Man, this garden of ours is refusing to give up this year. Went to the greenhouse expecting everything to have died down but instead, found a great bounty of peppers (Shishido, Bell and Banana), cucumbers, and tomatoes:
Made a tuna salad with the cucumber and tomatoes and it was sublime! The fresh and great scent of the cucumbers took me back to wonderful days of summer!
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The X16 is designed for rack mounting:
The only computer interface is Thunderbolt ()TB). It was hell getting TB capability on my PC motherboard. Once there, I had to buy a cable which at $40 (from Apple) for a 2.5 foot version, was outrageous. Then again the interface is running at ultra high-speed with very low latency so the passive cables are short by definition. This made it hard for me to see the display on the unit so I have no feedback on it. However, I did use the extensive software package/control that came with the unit, to the tune of 600 megabytes!
As the name indicates, you have 16 channels in and out:
DB-25 connectors are used so if you don't have such break out "snakes," you need to buy them as I did. They are commonly available. Just make sure the mating is correct. Mine was a no name $50 one for the ADC portion which worked fine. For the DAC functionality I used the additional monitor out so didn't need to buy that snake.
As you see, a hefty external power supply is used, reminding me of the original Xbox power supply. Not that you would want to mess with replacing it but note that it mates with a 4 pin, XLR like DC connector to the unit.
I ran into a major stumbling block in testing the X16 in that it only exposes an Audio interface for 64 bit applications. The Audio Precision software is 32 bits so would not see it at all. My Roon player did as did Adobe Audition. If you are going to use this for hi-fi applications, be sure your app is 64 bits. My solution to testing was using the AES input on the X16 for most of the measurements. I provide a dashboard readout using Thunderbolt by playing the test tone using Roon player.
This review is focused on electronic performance of the X16. There is tons and tons of functionality in the X16 that I won't touch on, nor am I qualified to do so. Please seek out other reviews for that functionality which is likely responsible for good bit of cost of this unit.
Lots of programming capability exists to set up the unit. Per recommendation from UA, I set the unit to 24 dBu output. The default is 20 dBu, with the extra voltage left for headroom. Fortunately performance is just as good at 20 dBu.
FYI I reviewed the measurements with UA and they are fine with the results.
Apollo X16 Measurements: DAC
Let's start with our usual dashboard pushing bits using Thunderbolt:
Note that I have heavily reduced the output level to our standard 4 volt output. We get stellar distortion rating of -135 dBFS (20 dB below threshold of hearing). Being designed for higher output voltage, the SINAD which includes noise and distortion, is excellent but slightly below the best we can get on our desktop DACs:
If we untie the wings from the X16 however to push higher output level, it reaches the same heights:
SINAD is now clocking at 120 dB. Note that this is driven by the sum of the Audio Precision analyzer noise and X16. If you subtract the former, you get close to what the company has specified (123 dB THD+N).
Performance is same for AES/EBU digital input:
I ran into another common bug in Audio Precision software in that it has some kind of buffer underrun which drops bits. This causes the measurements to get corrupted. To avoid this, I had to turn off averaging to get a single snapshot so ignore the more busy noise floor of the FFT. As you see, performance is identical so we will use AES from here on.
Here is our dynamic range:
Company spec is 127 dB but it is with a-weighting.
Distortion is kept to a minimum especially in low frequencies where there is usually a rise:
Intermodulation distortion vs level naturally varies a bit depending on the output voltage:
Linearity is absolutely nailed:
Filter response is typical but with excellent attenuation:
As you see, the bottom fell out of the graph!
Jitter and spurious tones are of course kept under control regardless of input type:
Finally, a very clean THD+N versus frequency despite its much wider 90 kHz bandwidth:
Apollo X16 Measurements: ADC
For the target market, analog conversion is everything so let's see our dashboard there:
This places the X16 high on the ladder but not the top:
Sweeping the input level shows that this is about the best we can get:
Notice the very low noise level (SINAD above is dominated by distortion). You can see this in better dynamic range than SINAD:
Here is a drill down of a 1 kHz tone relative to RME ADI-2 Pro (non-FS version):
As you see, it is the third harmonic which holds the X16 back (in red). On others it tends to be lower.
At lower than max input, the X16 competes at the top of the class:
I had no luck trying to get the ADC to operate at higher sample rates even though I changed it to higher values. Likely an operator error. So this test of frequency response is not that meaningful:
Finally, here is our THD+N versus frequency:
The much better results once again indicates a clean response above the audio band.
Conclusions
It would have been a watershed event if we had tested the X16 when it came out as it would left all of our high-fi DACs in the dust. In the interim period those companies razor focused on best measured performance and given us incredible performance. Still, the X16 if left to produce its high output, is able to keep up with them and of course provide incredible amount of additional functionality to say nothing of 16 channels input and output.
The high output of X16 should allow you to drive amplifiers such as Purifi and Hypex without their input buffers and get better measured performance than you can with high-fi DACs. But do keep in mind the complexity of using Thunderbolt for interface/programming and need for 64-bit player application.
It is my pleasure to put the Universal Audio Apollo X16 on my recommended list.
------------
As always, questions, comments, recommendations, etc. are welcome.
Man, this garden of ours is refusing to give up this year. Went to the greenhouse expecting everything to have died down but instead, found a great bounty of peppers (Shishido, Bell and Banana), cucumbers, and tomatoes:
Made a tuna salad with the cucumber and tomatoes and it was sublime! The fresh and great scent of the cucumbers took me back to wonderful days of summer!
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/