This is a complementary review of Sound Devices MixPre-3 II digital audio recorder and mixer.
@amirm has done a first review (you may find it here), but it appears he measured the device in "Basic" mode only.
This mode has some strong limitations.
One of those being that the limiters (there are several layers of them) are always active.
I will now have a look at the Advanced mode.
I rented the device for the week-end (45€) to measure it.
Ergonomy
One thing you may not realize immediately when looking at a photo of the device is how tiny it actually is.
Look at it on top of the RME UCX II.
The UCX II is half 19" rack width.
The device itself feels solid and quite heavy for its size.
A rubber-like coating prevents it to slip from any surface.
Critical knobs and commands are easy to recognize by touch.
The metal protrubation to the level knobs allows you to immediately sense the knob position in the dark.
Level knobs also have a ring that illuminates in Green or red, according to the input signal level.
You have a retracting 1/4" screw on top, to lock the device below a camera's tripod mounting hole.
And the hexagonal Alen key is included and attached to the MixPre rear.
Of course, the touch display is very small, and you need small fingers to operate it.
Navigating through all the options in the different menus is a different topic, though.
You need to really dig deep to find what you're looking for.
Also, the power switch is very small and hard to locate without looking.
Overall, this device's handling ergonomy is a mixed bag of quite well thought through controls... and messy ones.
Measurements
Given the limited time I had the device at hand, I decided to focus on Microphone input only.
This device is mainly a field recorder, so this is naturally its main focus point.
I also measured the Headphones output power, which is also of interest for field recording use.
Measurements were performed with my RME ADI-2/4 Pro SE, at various output levels, and with or without a Shure A15AS attenuator.
I use Virtins MultiInstrument 3.9.9.3 as a measurement software.
Noise and distortion measurements below are all for 20Hz-20kHz bandwidth.
EIN is measured with a 150ohm resistor at approx. 20°C.
As the device was rented, I didn't upgrade the firmware.
The firmware was 7.16 (build 3266)
I've setup Advanced mode.
This then gives me access to critical settings:
So I've set it up for 48kHz 32 bits float, limiters off.
I downloaded the ASIO driver and here we go.
ADC and Microphone input
Let's start with 2 measurements that summarize the 2 main saling points for this device
EIN at max Gain
This is a good value in general.
For a tiny portable device, it's exceptional.
Dynamic range at min gain
Waow !
Yes, that's an actual analog measurement
That's unsee, isn't it ?
(Actually, it matches specifications.)
And what is REALLY unseen is that it looks like both EIN and Dynamic range figures remain the same whatever the gain setting.
Well, there is a catch. Read on.
Signal path
I measured by sending the input signal to the USB interface "Pre fader".
You may see the path on this block diagram (source)
Let's zoom a bit on the input section
Now a word of explanation:
Usually, a Mic preamp interface has an analog preamp stage followed by the ADC.
And the analog preamp stage has a variable gain.
In this case, we see the ADC followed by a digital Trim (called "Gain" on the device screen). So it's not an analog gain.
This device is also using, per channel, multiple Mic Preamps and multiple ADC stages.
Their digital signal outputs are then combined in the digital domain, to mimic one single extra-wide dynamic range input.
Note that the exact number of Preamp and ADC stages is not documented, but given the measurement results here, I guess we have 2 preamp stages, each with its corresponding ADC.
You may see some hint of that if you vary the level:
At some point (around 78 mVrms input for a pure sine wave), you may see the SNR dropping abruptly.
This is where the device switches from one stage to another.
It is to be noted that this doesn't seem to be linked to 32 bits float operation: the device does the same in 24 bits.
32 bits float
So what's the benefit of 32 bits float ?
The benefit is that you may record above 0dBFS.
With an integer coding, your recording can't go above 0dBFS (dBFS=dB Full Scale)
With a float encoding, there is no such limit.
The big benefit is that you may push the level digitally, to allow proper level for monitoring through headphones, as an example, without any risk of saturation of the recording.
So this really allows to take full benefit of the dual stage preamp and ADC.
To operate the device, you just set the "gain" to the minimum value (6dB) and you forget it.
There is no need, like with most other Microphone preamps, to tune the gain to optimize noise and headroom.
Looks magic, doesn't it ?
Here is a plot of DR in 24 vs 32 bits (and the DR of the RME UCX II, which follows a "normal" pattern, for reference) for different "gain" levels
Input sensitivity range
So you have actually 2 sensitivities to remind: 78mV (-20dBu) for the first preamp stage, and 4.1V (14.6dBu) for the second stage.
SINAD dashboard at 4V, min gain
Well, all is not pink, unfortunately, and here start the bad news
As you can see above, the distortion is quite high (and mostly composed of odd harmonics).
Sure, that's almost matching the specs: 0,005% is 86dB SINAD (-86dB THD+N), but that's not very brilliant.
Worse: given the way this device works, you'll find similar level of distortion at low to medium level: just below 78mV, when you reach the maximum level for the first stage, you'll see similar distortion level.
But if we go over 78mV, we see distortion decreasing.
Look at the THD+N plot vs level, where you see the SNR drop, but also the THD increase when you approach the upper limit of the first stage, and the drop when switching to the second stage.
(From this plot, I couldn't identify any additional lower level step that would indicate a third stage is at play)
Also, we see a heavy saturation close to full scale.
This is actually the analog stage saturating for level >14.4dBu (-0.2dBFS at 6dB "gain")
Why Sound Devices didn't set the level 0.2dB lower to avoid this is beyond me !
This is just unacceptable, on an engineering point of view. (Even if, in practice, this isn't likely to have any effect. You don't record at 0dBFS)
IMD is doing the same
This is NOT GOOD.
OK, it's true that noise is more audible than distortion. But we're touching the level of distortion of your best microphones here.
So why to spend $x000(or more) per microphone to kill its performance by plugging it to a preamp with the same or worse distortion level ?
Note that above values are matching Amir's measurements
Frequency response
(There are some measurement artifacts here, especially just below 20kHz, due to the impossibility to synchroize perfectly the clock of the DAC with the clock of the ADC. Don't worry about those.)
Also not good: the Frequency response gives me a strange 0.7dB boost at low frequencies.
I double checked everything and couldn't find where this comes from.
This may be due to firmware, as Amir's measurements seem normal on that front.
Multitone 32
We see the same emphasis on low frequencies.
MT is not very clean.
This is just above the Preamp stage switching.
If we have a look just below, things get much worse:
Limiter measurement
I also measured the limiter on the Mic input
I measured both the level and the THD.
As one can see, the limiter doesn't prevent saturation above 4V.
Which is to be expected, since it looks to be working in the digital domain.
HPF measurement
There are also several High Pass Filter settings available.
Again, they are working in the digital domain, so won't prevent analog or ADC stage saturation due to plosives, wind or a shock.
Headphones amp measurements
Amir did test power with the limiters in place.
Here is a measurement with limiters set to "off".
Note that I couldn't have the DAC section working, so I fed the device from the Microphone inputs.
For power, this shouldn't make a difference, though.
I measured at 300 ohm and at 32 ohm.
Max power at 300 ohm was approx 18mW
At 32 ohm, distortion raises quickly. I stopped at 1%, where I could read 150mW.
The "hump" behavior at 300 ohm is likely due to the Mic preamp switching range.
Bottom line
As we already said about ergonomics, we have a mixed result.
The double stage architecture, combined with the capability to record in 32 bit float gives a lot of freedom for field recording.
The preamp noise performance is also pretty good.
Unfortunately, the ADC performance is not in line with those good results. The device performance is pretty poor on that aspect.
Also, the frequency response anomaly is just un-acceptable for a device of that price and pretentions. (That might be a firmware issue, though)
Personally, I wouldn't purchase this device for critical field recording.
I'd rather go with a more classic design, which will give better overall performance and more flexibility for a similar or lower price.
Your mileage may differ, though
@amirm has done a first review (you may find it here), but it appears he measured the device in "Basic" mode only.
This mode has some strong limitations.
One of those being that the limiters (there are several layers of them) are always active.
I will now have a look at the Advanced mode.
I rented the device for the week-end (45€) to measure it.
Ergonomy
One thing you may not realize immediately when looking at a photo of the device is how tiny it actually is.
Look at it on top of the RME UCX II.
The UCX II is half 19" rack width.
The device itself feels solid and quite heavy for its size.
A rubber-like coating prevents it to slip from any surface.
Critical knobs and commands are easy to recognize by touch.
The metal protrubation to the level knobs allows you to immediately sense the knob position in the dark.
Level knobs also have a ring that illuminates in Green or red, according to the input signal level.
You have a retracting 1/4" screw on top, to lock the device below a camera's tripod mounting hole.
And the hexagonal Alen key is included and attached to the MixPre rear.
Of course, the touch display is very small, and you need small fingers to operate it.
Navigating through all the options in the different menus is a different topic, though.
You need to really dig deep to find what you're looking for.
Also, the power switch is very small and hard to locate without looking.
Overall, this device's handling ergonomy is a mixed bag of quite well thought through controls... and messy ones.
Measurements
Given the limited time I had the device at hand, I decided to focus on Microphone input only.
This device is mainly a field recorder, so this is naturally its main focus point.
I also measured the Headphones output power, which is also of interest for field recording use.
Measurements were performed with my RME ADI-2/4 Pro SE, at various output levels, and with or without a Shure A15AS attenuator.
I use Virtins MultiInstrument 3.9.9.3 as a measurement software.
Noise and distortion measurements below are all for 20Hz-20kHz bandwidth.
EIN is measured with a 150ohm resistor at approx. 20°C.
As the device was rented, I didn't upgrade the firmware.
The firmware was 7.16 (build 3266)
I've setup Advanced mode.
This then gives me access to critical settings:
So I've set it up for 48kHz 32 bits float, limiters off.
I downloaded the ASIO driver and here we go.
ADC and Microphone input
Let's start with 2 measurements that summarize the 2 main saling points for this device
EIN at max Gain
This is a good value in general.
For a tiny portable device, it's exceptional.
Dynamic range at min gain
Waow !
Yes, that's an actual analog measurement
That's unsee, isn't it ?
(Actually, it matches specifications.)
And what is REALLY unseen is that it looks like both EIN and Dynamic range figures remain the same whatever the gain setting.
Well, there is a catch. Read on.
Signal path
I measured by sending the input signal to the USB interface "Pre fader".
You may see the path on this block diagram (source)
Let's zoom a bit on the input section
Now a word of explanation:
Usually, a Mic preamp interface has an analog preamp stage followed by the ADC.
And the analog preamp stage has a variable gain.
In this case, we see the ADC followed by a digital Trim (called "Gain" on the device screen). So it's not an analog gain.
This device is also using, per channel, multiple Mic Preamps and multiple ADC stages.
Their digital signal outputs are then combined in the digital domain, to mimic one single extra-wide dynamic range input.
Note that the exact number of Preamp and ADC stages is not documented, but given the measurement results here, I guess we have 2 preamp stages, each with its corresponding ADC.
You may see some hint of that if you vary the level:
At some point (around 78 mVrms input for a pure sine wave), you may see the SNR dropping abruptly.
This is where the device switches from one stage to another.
It is to be noted that this doesn't seem to be linked to 32 bits float operation: the device does the same in 24 bits.
32 bits float
So what's the benefit of 32 bits float ?
The benefit is that you may record above 0dBFS.
With an integer coding, your recording can't go above 0dBFS (dBFS=dB Full Scale)
With a float encoding, there is no such limit.
The big benefit is that you may push the level digitally, to allow proper level for monitoring through headphones, as an example, without any risk of saturation of the recording.
So this really allows to take full benefit of the dual stage preamp and ADC.
To operate the device, you just set the "gain" to the minimum value (6dB) and you forget it.
There is no need, like with most other Microphone preamps, to tune the gain to optimize noise and headroom.
Looks magic, doesn't it ?
Here is a plot of DR in 24 vs 32 bits (and the DR of the RME UCX II, which follows a "normal" pattern, for reference) for different "gain" levels
Input sensitivity range
So you have actually 2 sensitivities to remind: 78mV (-20dBu) for the first preamp stage, and 4.1V (14.6dBu) for the second stage.
SINAD dashboard at 4V, min gain
Well, all is not pink, unfortunately, and here start the bad news
As you can see above, the distortion is quite high (and mostly composed of odd harmonics).
Sure, that's almost matching the specs: 0,005% is 86dB SINAD (-86dB THD+N), but that's not very brilliant.
Worse: given the way this device works, you'll find similar level of distortion at low to medium level: just below 78mV, when you reach the maximum level for the first stage, you'll see similar distortion level.
But if we go over 78mV, we see distortion decreasing.
Look at the THD+N plot vs level, where you see the SNR drop, but also the THD increase when you approach the upper limit of the first stage, and the drop when switching to the second stage.
(From this plot, I couldn't identify any additional lower level step that would indicate a third stage is at play)
Also, we see a heavy saturation close to full scale.
This is actually the analog stage saturating for level >14.4dBu (-0.2dBFS at 6dB "gain")
Why Sound Devices didn't set the level 0.2dB lower to avoid this is beyond me !
This is just unacceptable, on an engineering point of view. (Even if, in practice, this isn't likely to have any effect. You don't record at 0dBFS)
IMD is doing the same
This is NOT GOOD.
OK, it's true that noise is more audible than distortion. But we're touching the level of distortion of your best microphones here.
So why to spend $x000(or more) per microphone to kill its performance by plugging it to a preamp with the same or worse distortion level ?
Note that above values are matching Amir's measurements
Frequency response
(There are some measurement artifacts here, especially just below 20kHz, due to the impossibility to synchroize perfectly the clock of the DAC with the clock of the ADC. Don't worry about those.)
Also not good: the Frequency response gives me a strange 0.7dB boost at low frequencies.
I double checked everything and couldn't find where this comes from.
This may be due to firmware, as Amir's measurements seem normal on that front.
Multitone 32
We see the same emphasis on low frequencies.
MT is not very clean.
This is just above the Preamp stage switching.
If we have a look just below, things get much worse:
Limiter measurement
I also measured the limiter on the Mic input
I measured both the level and the THD.
As one can see, the limiter doesn't prevent saturation above 4V.
Which is to be expected, since it looks to be working in the digital domain.
HPF measurement
There are also several High Pass Filter settings available.
Again, they are working in the digital domain, so won't prevent analog or ADC stage saturation due to plosives, wind or a shock.
Headphones amp measurements
Amir did test power with the limiters in place.
Here is a measurement with limiters set to "off".
Note that I couldn't have the DAC section working, so I fed the device from the Microphone inputs.
For power, this shouldn't make a difference, though.
I measured at 300 ohm and at 32 ohm.
Max power at 300 ohm was approx 18mW
At 32 ohm, distortion raises quickly. I stopped at 1%, where I could read 150mW.
The "hump" behavior at 300 ohm is likely due to the Mic preamp switching range.
Bottom line
As we already said about ergonomics, we have a mixed result.
The double stage architecture, combined with the capability to record in 32 bit float gives a lot of freedom for field recording.
The preamp noise performance is also pretty good.
Unfortunately, the ADC performance is not in line with those good results. The device performance is pretty poor on that aspect.
Also, the frequency response anomaly is just un-acceptable for a device of that price and pretentions. (That might be a firmware issue, though)
Personally, I wouldn't purchase this device for critical field recording.
I'd rather go with a more classic design, which will give better overall performance and more flexibility for a similar or lower price.
Your mileage may differ, though
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