American manufacturer of professional audio equipment MOTU has released two mass-market low-cost USB 2.0 audio interfaces, MOTU M2 and M4. The models are basically the same, except that the upper M4 has two more line inputs and outputs. So everything we said in our MOTU M4 review also applies to the MOTU M2 (although we have a separate detailed review on the M2). These audio interfaces are interesting because they inherit the flagship ESS Sabre32 Ultra™ DAC and color LCD screen with peak meters. Previously, there were no such products in this price range, so MOTU's interfaces created a lot of "noise & hype" in the music production community.
Before we get into the main part of our review, let's take a look at the MOTU M4's specs to get a better understanding of all of its features.
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Best Price on MOTU M4 Audio Interface
The MOTU M4 is one of the best 4-I/O interfaces in its price range. Elite-level sound quality, pro-style metering, and versatile I/O make it ideal for musicians, streamers, producers, etc. |
Classic Package
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In the official presentation at NAMM'2020, the company representative announced a few key points. Here we can see that the company is really focusing on three things: DAC, low latency, and peak meters. As for RTL latency, it is only listed here for 96 kHz mode, the value is 2.5 ms. MOTU has faster interfaces with lower latency, but in reality, there are very few scenarios where this is critical to the user. For example, MOTU's 8pre-es interface has a Thunderbolt connection latency of only 1.6ms, but let's face it, that's the last number anyone cares about. First of all, such interfaces are bought in the studio to get 8 microphone preamps and the possibility of cascading, i.e., easily increasing the number of channels by 2, 3, or 4 times compared to the existing ones. The large number of channels (e.g. 128) is critical for such studios. If the unit also processes all channels quickly, it's a pleasure. But it is still better not to set the buffer to 32 samples to avoid random clicks in the signal. MOTU rightly recommends setting the buffer to 256 samples.
Peak meters on the MOTU M2/M4 are an added convenience, but not critically important. First, modern DAW programs allow you to display the mixer on a separate monitor and conveniently view all input and output channels. This is convenient for both recording and editing. Peak meters on the device itself are still a feature of more expensive interfaces, where it is important to see the signal coming through the digital buses. That's why inexpensive products usually have only one overload indicator or 3-4 level indication segments.
The main advantage of the audio interfaces can be seen in the ESS Sabre 32 converters. The ES9016S chip is used specifically, just like in MOTU's flagship models. This is a very interesting choice. Usually, manufacturers divide their products into niches. So that the junior models do not interfere with the promotion of the flagship models, they put converters there that are called "simpler". This is quite justified, as the casual user will still connect such an interface to inexpensive monitors or headphones, where the model of the DAC chip does not play a special role. In addition, modern monitors tend to use Class D amplifiers with ADC on the line input, so the DAC class has even less influence. However, some users would like to see better converters than those found in entry-level models. Just remember that the final sound quality is influenced by too many factors. This means that even if the equipment is similar, the quality can be very different. Therefore, each situation must be considered on its own merits. High-quality electronics are a necessary but not sufficient condition for good sound.
Inside the MOTU M4 audio interface, we see a modern XMOS XU216 microcontroller that serves the USB 2.0 bus and outputs digital data to the converter chips. Interestingly, the USB-C connector is chosen as the more modern one. But the bus version is definitely USB 2.0. It is also the most common and compatible today.
The 4-channel ADC is an AK5554 chip from the modern 55 series, which supports formats up to 32-bit 768 kHz, but in this product it works up to 192 kHz. The dynamic range is 115dB and the Kg+noise is -106dB. These are not record-breaking figures, but they are much higher than interfaces of this level.
The DAC is an 8-channel ES9016S. It is a very good and not cheap chip with 124 dBA dynamic range and Kg+noise -110 dB. At the moment, as we know, newer versions of the ESS Sabre 32 family have already been released, but they cost several times more. Therefore, the choice of the manufacturer can be called optimal.
It's rather strange that the headphone output is served by an OPA1688 operational amplifier. It produces 50 mW at 32 ohms with low distortion. Although these numbers seem a bit weak for an amplifier, some cheap interface manufacturers manage to reduce the output power by a factor of 10. Even with high-impedance headphones, the volume is more than adequate, and the 3.3Vrms signal sweep in the Beyerdynamic DT 990 PRO is quite good, with no audible problems.
It should be said that modern audio interfaces, even inexpensive ones, have pretty good microphone preamps. It is difficult to surprise the user, but MOTU engineers managed it. The THAT 6263 is a very interesting American microphone preamplifier with digital control, combining a preamplifier, controller, and ADC buffer. The gain range is -8dB to +34dB. Apparently, there is an additional gain stage inside.
One more thing. The interface is designed and manufactured in the USA at a factory in Massachusetts. Despite the high cost of manufacturing in the USA, the MOTU M4 has an excellent price-quality ratio and is not expensive.
RTL latency with a 64-sample buffer is a fairly standard 8ms, which is typical for most USB 2.0 interfaces. However, with 32 samples, the latency drops dramatically to 5ms. Most likely, ASIO buffers reduce the buffer size for secure data transfer over the USB bus. In 96 kHz mode, the latency is even lower - less than 3 ms. This 32-sample mode is good for advertising, but for work it's better to set 64 samples and higher if you don't want to hear crackling in the sound or samples disappearing during recording due to a lack of CPU power.
Testing the MOTU M4 with microphoneWe connected a Neumann TLM 102 condenser microphone to evaluate the recording quality. As always, we compared it to our "reference point", the TASCAM UH-7000, which has very well sounding neutral preamps on the OPA1612A.
The quality of the MOTU M4's microphone preamps can be described as very good. It seemed to us that the sound on the recording had a slight accent in the midrange, and was a bit brighter in the presence range. This has a good effect when connecting inexpensive condenser mics, giving them a livelier sound without the need to equalize the 2kHz range or saturate them with plug-ins. The sound is immediately spectacular, but without excessive harshness or any audible distortion.
The most unexpected thing we found while using the MOTU M4 was that absolutely all of its controls/encoders are digital! To be precise, the controls themselves are no different from analog variable resistors, but all parameters - input signal level, line output volume, headphone output volume - change logarithmically, in 1 dB steps, simultaneously in both channels. At the same time, the controls have no clicks like digital encoders, and the controls themselves have stops and a mark of the current position. Most likely, these are ordinary variable resistors connected to the DC ADC of the microcontroller. The advantage of this solution is that you can set all input and output channels to exactly the same level. There will never be a skew between the right and left channels at any level. This is just a HUGE operational plus!
The downside is that you can't see the current volume level in dB and the gain in dB - there's nothing on the screen except for rather useless peak meters. And these peak meters only show the digital signal level up to the control, i.e., they don't depend on the current position of the line output encoder. It would have been nice to see markings in dB next to the encoders, like on inexpensive mixing consoles (at least in tens of dB increments). Unfortunately, there are no markings. Another peculiarity is that the headphone output is exactly the same as channels 1-2. There is no way to output channels 3-4. That's strange, because the headphones obviously use separate channels of the ESS DAC, with individual level control. It doesn't cost anything to reassign them, but the card has no control software or configuration panel.
In general, we felt that the MOTU M4 was a test version of MOTU's flagship professional interfaces, the MOTU 624 and above, where everything is perfectly done and there are no such shortcomings. For example, on the 624, as soon as you touch the headphone encoder, the screen immediately says PHONE VOL -3.0 dB. Also, the older MOTU has a powerful hardware effects processor and control of the mixer and other things from the iPad, the ability to connect multiple units into a single system. So it's a whole different class of hardware. The MOTU M4 is just a 2-4 channel input and output for personal use. And that's where the manufacturer gets a lot of credit.
When it comes to the sound quality of the line output, the MOTU M4 deserves a lot of praise. It is the clear leader in this price category. The sound is just wonderful. We connected our ADAM active monitors both to the TSR outputs and to the XLR inputs in the monitors, and the RCA outputs to the RCA inputs. In both cases, the sound is very good. Good detail, wide open, no distortion. You get the feeling that MOTU has decided to reduce all features as much as possible, but to seduce the user with high-quality sound. The headphone output is also very good. It's not record-breaking, but it's good enough for most headphones.
Finally, we've reached the end of our MOTU M4 review, it's time to summarize the results. Congratulations to MOTU for creating a great low-cost product for home use. For studio work, the M4 has pretty good preamps and ADCs that are better than entry-level units. We also note good connectivity for both TRS and RCA.
But all these trifles can be forgiven for the excellent sound quality on the line and headphone outputs. Good electronic stuffing and DAC ESS Sabre 32 here is not "for a tick", but really brings great benefit. We were even more pleased with the really affordable price of the product. This makes it attractive even for those who only listen to music and only occasionally record something themselves. However, professional musicians should increase their budget and look at the older models of MOTU interfaces, which are much more interesting for the recording studio.
We hope you enjoyed our review of the MOTU M4 audio interface. Please feel free to leave your comments, questions, and suggestions in the section below. We will be happy to answer them all as soon as possible. If you already own MOTU M4 and have used it for a while, don't forget to share your impressions and tell us what you liked or disliked about this audio interface.
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9.3
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Our Score
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