Hello Everyone,
This is a review and detailed measurements of the Moondrop Discdream 2 ULTRA portable CD player.
Moondrop Discdream 2 ULTRA - Presentation
I'm not sure I need to provide an extensive presentation as everything is available on the vendor's website. In a nutshell, this is a portable CD player that plays on batteries and offers the option to use its internal DAC from a PC (USB input).
I like the fact it offers unbalanced and balanced outputs, as well as a digital one via a a single 3.5mm jack output. Note that no 3.5mm to RCA coax nor optical converter are provided, so you'll need to buy some to use the digital outputs.
The Discdream is bigger and heavier than the Fiio DM13 that I recently reviewed, and that is less of my taste. But, it will spin a CD when opened, and that is cool:
Moondrop Discdream 2 ULTRA - Measurement (Analog out)
I performed all measurements as I described them in the post “More than we hear”, and as I reported them for the Onkyo C-733 review. Over time, this will help comparing the devices I reviewed.
The Moondrop Discdream 2 ULTRA outputs a 4Vrsm from balanced outputs (I did not test unbalanced). There was a slight channel imbalance of 0.06dB which is good. The balanced outputs are noninverting. All the below measurements are from balanced output with volume set at maximum.
Let's start with the standard 999.91Hz sine @0dBFS (without dither) from the test CD:
The Discdream is in par with its published specs (0.0016%). The resolution is indeed 16bits.
The results are surprisingly nearly identical similar to what I measured with the Fiio DM13. We find the exact same series of odd harmonics (H3, H5, H7, ...). Again, that reminded me of some issue we already discussed here when trying the burn a test CD with Windows Media Player. The distorsion you see here does not come from the conversion itself... So this is a repeat of the DM13 story, except that here we also have an H2 that was absent with the DM13.
As usual this is the same measurement (999.91Hz) at -6dBFS:
We have a repeat of the distorsion profile (odd harmonics slowly decreasing) at a lower level too, that is very uncommon. The similarities with the DM13 tells me that a common path prior to conversion is taken here. This means there is some sort of level equalization as we saw with WMP, in digital domain, and again exactly as I reported with the Fiio DM13. Using shaped dither, we can lower the noise floor to analyze deeper, as I did too with the Fiio.
Below is the same 999.91Hz @0dBFS but with shaped dither (hence the double wave of low level noise you see starting at 6kHz):
To the exception of the H2, this is the exact same trace as the one of the Fiio DM13. Despite a significant price gap, we get the same performance...
Let's go to the good news. First, this is an very silent player:
There's no trace of mains component (50Hz), which is a pleasure to see.
Let's continue with the bandwidth that is very flat:
You can see the channel mismatch (0.06dB) which is not a concern.
Let's have a look at the oversampling filter efficiency:
The oversampling filter is slightly better than the one of the Fiio DM13, as the noise shaping technique shows its effect later in frequency. That means there's a different filter in use here.
That said, look at the spikes I pointed out. I don't know what they are. Using the Discdream as a DAC, I could see that all of them are harmonics of 8kHz. So are they the USB 8kHz PHY Microframe Packet Noise? I can't be sure but this is weird. Let's have look at a 999.91Hz @0dBFS from USB input to know more (linear frequency scale from 20Hz to 80kHz):
This is not nice at all. I added the dashboard for you to see that used as DAC, we barely get a resolution of 17bits because of all that distortion. For that reason, I will not be talking much about using the Discdream as a DAC, other than to say it's only a continuity plan is case of a major crash of your main DAC. It is to note, though, that the clock in use when connecting via USB is not the same (Moondrop talks about 3 clocks in the device) and is much less precise than in CD mode.
There was nothing I could do to suppress these 8kHz and associated harmonics which are constantly here. Usually, when I encounter issues that I believe related to USB or noise from mains, I use a Topping HS02 USB isolator. But for some reasons, when trying to use it, it cut the communication between the PC and the Discdream. Some of you more into computer science than me might know the reason. I never suffered such an issue previously. Maybe a firmware update can fix some of the issues.
Well, let's continue to use and measure the Discdream as a CD player. This is below the standard multitone test:
Back to go news, the Discdream has no issue to achieve more than 16bits free of distortion .
The jitter test shows a perfect result:
Nailed!
Started with the Teac VRDS-20 review, and on your request + support to get it done (more here), I'm adding an "intersample-overs" test which intends to identify the behavior of the digital filtering and DAC when it come to process near clipping signals. Because of the oversampling, there might be interpolated data that go above 0dBFS and would saturate (clip) the DAC and therefore the output. And this effect shows through distorsion (THD+N measurement up to 96kHz):
I kept some references and will keep the same for other reviews, so you can quickly compare. The results of the Moondrop Discdream 2 ULTRA mean the oversampling filter does not have headroom. That said, if I lower the volume by 1 step, I get 1dB headroom and so on. That means the volume attenuation is done in digital domain prior to conversion, which means when listening to the Discdream with your headset, you will never suffer inter sample overs.
Let's move one to a test that Stereophile was often performing, and that I like a lot too. It is from an undithered 997Hz sine at -90.31dBFS. With 16bits, the signal should appear (on a scope) as the 3DC levels of the smallest symmetrical sign magnitude digital signal, after conversion. Here is the result with the Discdream:
This is as ugly as with the Fiio DM13. Again very strange to find the exact same results.
What we see here is asymmetry of the output that I've never seen before (except with the Fiio DM13). This view means the output is far from the requested -90.31dBFS, and actually I measured it at -95.41dBFS. So that is a lack of linearity by 5dB, and that is huge!
Fact is the DM13 looses linearity as early as -70dBFS (by 0.8dB), while we are used to see linearity nailed down to -120dBFS these days! This is equivalent to what I saw with the Marantz CD-73, which had a 14bits DAC. So this is really bad results for the Discdream, and again exactly what I saw with the Fiio DM13.
So we have the culprit here, I believe. There is processing of the signal which deteriorates it at low levels and that is too bad.
Other measurements (not shown):
Moondrop Discdream 2 ULTRA - Testing the drive
What would be good measurements if the drive would not properly read a slightly scratched CD, or one that was created at the limits of the norm? The below tests reply to these questions.
The drive was able to consistently continue playing, and without generating typical digital clicks, with dropouts of up to 3mm. The interpolation effect remained hidden to my hears when it kicked-off and the Discdream did not fail to maintain a constant flow with up to 4mm dropouts. It is the maximum I can measure, so that is near perfection. The Fiio had no issue with variable linear velocity and/or track pitch, as well as with HF detection. This is a crazy good drive!
Fiio DM13 - Measurements (Optical Out)
I've seen several of you reviewing CD players using their digital outputs, in case the results could be improved from an external DAC.
The precision of the clock meant it was easy to get a clean FFT (there's no PLL with the digital receiver when I run this measurement, which makes it a challenge most of the time). I got the below (999.91Hz @0dBFS):
We find again the distorsion that I already showed before, with a set of odd harmonics that are not on the test CD (note the absence of the H2 this time). This means there is digital modification of the signal. This is not "bit perfect" by far.
By the way, our 3DC levels are also impacted, this is again asymmetry and therefore lack of linearity in the digital domain:
This is bad and same as the DM13.
I think the drive of the Moondrop could have been one of the best I tested, if only the digital signal was not impacted by some processing.
Conclusion
The Moondrop Discdream is extremely good at reading a scratched CD and following a track without failing. It's the best I measured (with the Fiio DM13) in that area. It's the only player (of 2) able to read correctly with 3mm dropouts on the disc and only 1 click with 4mm, amazing!
It is therefore too bad to see such digital processing and degradation of the signal. I think this is a software issue and I hope a firmware can fix that. I will update if that's the case.
In the meantime, I can't say the flaws shown can be heard. They remained hidden to my hears. But this little player missed a very high mark because of some (undesired) processing. Too bad.
PS: Message to Moondrop engineering: Please fix that software error with digital attenuation calculation (at least at full scale), and you have the best CD Player/Transport of all times (with a good clock). Pretty please?
This is a review and detailed measurements of the Moondrop Discdream 2 ULTRA portable CD player.
Moondrop Discdream 2 ULTRA - Presentation
I'm not sure I need to provide an extensive presentation as everything is available on the vendor's website. In a nutshell, this is a portable CD player that plays on batteries and offers the option to use its internal DAC from a PC (USB input).
I like the fact it offers unbalanced and balanced outputs, as well as a digital one via a a single 3.5mm jack output. Note that no 3.5mm to RCA coax nor optical converter are provided, so you'll need to buy some to use the digital outputs.
The Discdream is bigger and heavier than the Fiio DM13 that I recently reviewed, and that is less of my taste. But, it will spin a CD when opened, and that is cool:
Moondrop Discdream 2 ULTRA - Measurement (Analog out)
I performed all measurements as I described them in the post “More than we hear”, and as I reported them for the Onkyo C-733 review. Over time, this will help comparing the devices I reviewed.
The Moondrop Discdream 2 ULTRA outputs a 4Vrsm from balanced outputs (I did not test unbalanced). There was a slight channel imbalance of 0.06dB which is good. The balanced outputs are noninverting. All the below measurements are from balanced output with volume set at maximum.
Let's start with the standard 999.91Hz sine @0dBFS (without dither) from the test CD:
The Discdream is in par with its published specs (0.0016%). The resolution is indeed 16bits.
The results are surprisingly nearly identical similar to what I measured with the Fiio DM13. We find the exact same series of odd harmonics (H3, H5, H7, ...). Again, that reminded me of some issue we already discussed here when trying the burn a test CD with Windows Media Player. The distorsion you see here does not come from the conversion itself... So this is a repeat of the DM13 story, except that here we also have an H2 that was absent with the DM13.
As usual this is the same measurement (999.91Hz) at -6dBFS:
We have a repeat of the distorsion profile (odd harmonics slowly decreasing) at a lower level too, that is very uncommon. The similarities with the DM13 tells me that a common path prior to conversion is taken here. This means there is some sort of level equalization as we saw with WMP, in digital domain, and again exactly as I reported with the Fiio DM13. Using shaped dither, we can lower the noise floor to analyze deeper, as I did too with the Fiio.
Below is the same 999.91Hz @0dBFS but with shaped dither (hence the double wave of low level noise you see starting at 6kHz):
To the exception of the H2, this is the exact same trace as the one of the Fiio DM13. Despite a significant price gap, we get the same performance...
Let's go to the good news. First, this is an very silent player:
There's no trace of mains component (50Hz), which is a pleasure to see.
Let's continue with the bandwidth that is very flat:
You can see the channel mismatch (0.06dB) which is not a concern.
Let's have a look at the oversampling filter efficiency:
The oversampling filter is slightly better than the one of the Fiio DM13, as the noise shaping technique shows its effect later in frequency. That means there's a different filter in use here.
That said, look at the spikes I pointed out. I don't know what they are. Using the Discdream as a DAC, I could see that all of them are harmonics of 8kHz. So are they the USB 8kHz PHY Microframe Packet Noise? I can't be sure but this is weird. Let's have look at a 999.91Hz @0dBFS from USB input to know more (linear frequency scale from 20Hz to 80kHz):
This is not nice at all. I added the dashboard for you to see that used as DAC, we barely get a resolution of 17bits because of all that distortion. For that reason, I will not be talking much about using the Discdream as a DAC, other than to say it's only a continuity plan is case of a major crash of your main DAC. It is to note, though, that the clock in use when connecting via USB is not the same (Moondrop talks about 3 clocks in the device) and is much less precise than in CD mode.
There was nothing I could do to suppress these 8kHz and associated harmonics which are constantly here. Usually, when I encounter issues that I believe related to USB or noise from mains, I use a Topping HS02 USB isolator. But for some reasons, when trying to use it, it cut the communication between the PC and the Discdream. Some of you more into computer science than me might know the reason. I never suffered such an issue previously. Maybe a firmware update can fix some of the issues.
Well, let's continue to use and measure the Discdream as a CD player. This is below the standard multitone test:
Back to go news, the Discdream has no issue to achieve more than 16bits free of distortion .
The jitter test shows a perfect result:
Nailed!
Started with the Teac VRDS-20 review, and on your request + support to get it done (more here), I'm adding an "intersample-overs" test which intends to identify the behavior of the digital filtering and DAC when it come to process near clipping signals. Because of the oversampling, there might be interpolated data that go above 0dBFS and would saturate (clip) the DAC and therefore the output. And this effect shows through distorsion (THD+N measurement up to 96kHz):
| Intersample-overs tests Bandwidth of the THD+N measurements is 20Hz - 96kHz | 5512.5 Hz sine, Peak = +0.69dBFS | 7350 Hz sine, Peak = +1.25dBFS | 11025 Hz sine, Peak = +3.0dBFS |
| Teac VRDS-20 | -30.7dB | -26.6dB | -17.6dB |
| Yamaha CD-1 | -84.6dB | -84.9dB | -78.1dB |
| Denon DCD-900NE | -34.2dB | -27.1dB | -19.1dB |
| Denon DCD-SA1 | -33.6dB | -27.6dB | -18.3dB |
| Onkyo C-733 | -88.3dB | -40.4dB | -21.2dB |
| Denon DCD-3560 | -30.2dB | -24.7dB | -17.4dB |
| Marantz CD-73 | -50.3dB | -52.0dB | -27.7dB |
| Fiio DM13 (-3dB attenuation output) | -57.5dB (-91.6dB) | -58.2dB (-78.1dB) | -58.4dB (-81dB) |
| Moondrop Discdream 2 ULTRA | -38.7dB | -28dB | -18.4dB |
I kept some references and will keep the same for other reviews, so you can quickly compare. The results of the Moondrop Discdream 2 ULTRA mean the oversampling filter does not have headroom. That said, if I lower the volume by 1 step, I get 1dB headroom and so on. That means the volume attenuation is done in digital domain prior to conversion, which means when listening to the Discdream with your headset, you will never suffer inter sample overs.
Let's move one to a test that Stereophile was often performing, and that I like a lot too. It is from an undithered 997Hz sine at -90.31dBFS. With 16bits, the signal should appear (on a scope) as the 3DC levels of the smallest symmetrical sign magnitude digital signal, after conversion. Here is the result with the Discdream:
This is as ugly as with the Fiio DM13. Again very strange to find the exact same results.
What we see here is asymmetry of the output that I've never seen before (except with the Fiio DM13). This view means the output is far from the requested -90.31dBFS, and actually I measured it at -95.41dBFS. So that is a lack of linearity by 5dB, and that is huge!
Fact is the DM13 looses linearity as early as -70dBFS (by 0.8dB), while we are used to see linearity nailed down to -120dBFS these days! This is equivalent to what I saw with the Marantz CD-73, which had a 14bits DAC. So this is really bad results for the Discdream, and again exactly what I saw with the Fiio DM13.
So we have the culprit here, I believe. There is processing of the signal which deteriorates it at low levels and that is too bad.
Other measurements (not shown):
- IMD AES-17 DFD "Analog" (18kHz & 20kHz 1:1) : -90.3dB
- IMD AES-17 DFD "Digital" (17'987Hz & 19'997Hz 1:1) : -93.5dB
- IMD AES-17 MD (41Hz & 7993Hz 4:1): -97.2dB
- IMD CCIF (19kHz & 20kHz 1:1) : -93dB
- Dynamic Range : 98dB
- Crosstalk: below -150dB
- Pitch Error : 19'997.09Hz (19'997Hz requested) ie (5ppm)
Moondrop Discdream 2 ULTRA - Testing the drive
What would be good measurements if the drive would not properly read a slightly scratched CD, or one that was created at the limits of the norm? The below tests reply to these questions.
| Test type | Technical test | Results |
| Variation of linear cutting velocity | From 1.20m/s to 1.40m/s | Pass |
| Variation of track pitch | From 1.5µm to 1.7µm | Pass |
| Combined variations of track pitch and velocity | From 1.20m/s & 1.5µm to 1.40m/s & 1.7µm | Pass |
| HF detection (asymmetry pitch/flat ratio) | Variation from 2% to 18% | Pass |
| Dropouts resistance | From 0.05mm (0.038ms) to 4mm (3.080ms) | Up to 3mm. |
| Combined dropouts and smallest pitch | From 1.5µm & 1mm to 1.5µm & 2.4mm | Pass |
| Successive dropouts | From 2x0.1mm to 2x3mm | Pass |
The drive was able to consistently continue playing, and without generating typical digital clicks, with dropouts of up to 3mm. The interpolation effect remained hidden to my hears when it kicked-off and the Discdream did not fail to maintain a constant flow with up to 4mm dropouts. It is the maximum I can measure, so that is near perfection. The Fiio had no issue with variable linear velocity and/or track pitch, as well as with HF detection. This is a crazy good drive!
Fiio DM13 - Measurements (Optical Out)
I've seen several of you reviewing CD players using their digital outputs, in case the results could be improved from an external DAC.
The precision of the clock meant it was easy to get a clean FFT (there's no PLL with the digital receiver when I run this measurement, which makes it a challenge most of the time). I got the below (999.91Hz @0dBFS):
We find again the distorsion that I already showed before, with a set of odd harmonics that are not on the test CD (note the absence of the H2 this time). This means there is digital modification of the signal. This is not "bit perfect" by far.
By the way, our 3DC levels are also impacted, this is again asymmetry and therefore lack of linearity in the digital domain:
This is bad and same as the DM13.
I think the drive of the Moondrop could have been one of the best I tested, if only the digital signal was not impacted by some processing.
Conclusion
The Moondrop Discdream is extremely good at reading a scratched CD and following a track without failing. It's the best I measured (with the Fiio DM13) in that area. It's the only player (of 2) able to read correctly with 3mm dropouts on the disc and only 1 click with 4mm, amazing!
It is therefore too bad to see such digital processing and degradation of the signal. I think this is a software issue and I hope a firmware can fix that. I will update if that's the case.
In the meantime, I can't say the flaws shown can be heard. They remained hidden to my hears. But this little player missed a very high mark because of some (undesired) processing. Too bad.
PS: Message to Moondrop engineering: Please fix that software error with digital attenuation calculation (at least at full scale), and you have the best CD Player/Transport of all times (with a good clock). Pretty please?
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