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This is a review and measurements of the M-Audio M-Track Solo audio interface. It is very much a budget offering, costing around $40 on Amazon US. I bought it for myself as a cheap interface for my bass guitar, but as you'll see from the results it can't do that job. On the other hand it is usable as a cheap low resolution digital-only interface so long as you recognise the specs are complete hallucinations.
No panthers here in Australia, but I will give it a two quokka rating out of five just because it's so cheap.
M-Audio quote between -94dB and -86dB THD+N (A weighted) for the various inputs, which is wildly optimistic. Noise alone is -93dBFS(A) a minimum gain, which limits us to 14.5bits of resolution out of the gate. After sweeping them all to find the optimal scenario I was able to get -87dBFS(A) from the right TRS input at 1.2V/+4dBu, but it was at a -9dBFS signal level so the SNR was only -78dB. You can increase the level but distortion goes up, or increase the gain but noise goes up. Here are the sweeps at mainly zero gain, which show the domination of noise until we get into a narrow sweet spot, then followed by a rapid increase in distortion.
Here's the 1kHz FFT for input 2 at the best settings I could achieve.
There are some strange wobbles in the frequency response on all inputs - only +-0.1dB at 2kHz-8kHz, but then getting bigger and leading to a -2dB drop at 20KHz:
This odd behaviour also shows up in the multitone test:
Overall the ADC performance is disappointing.
The RCA output gets to 750mV/0dBU so it meets its spec for output voltage but is noisy:
No panthers here in Australia, but I will give it a two quokka rating out of five just because it's so cheap.
What do you get?
- USB in and out at 48k/16bit
- Two analog inputs, available as L/R on the USB interface
- Input 1/Left is a combo XLR and TRS, with the XLR being higher gain than the TRS. There's also phantom power available on the XLR input
- Input 2/Right is a TRS with switchable gain via a "Line/Inst" switch
- Monitoring:
- Headphone out on the front from a 3.5mm TRS
- Line out on the back from 2 x RCA which are in reality the same as it's not a stereo device
- A switch to choose between using the USB input for monitoring or "Direct" monitoring of the input signal
- Input gain knobs
- An output level control
Build quality
The overall package is lightweight but solid. The case is all plastic with screws tying the top/back to the main body. This isn't going to fall apart in a hurry. Taking it apart reveals decent circuit board construction for the price, with sockets secured with through-hole soldering and/or pegs. On the other hand I had to get a second sample because the first one developed a fault in the left input, but that might have been down to abusing it a bit during testing.Performance as an ADC
Unless otherwise specified all measurements are taken at 48KHz/16bit input which is the limit of the USB interface. A Topping D10 balanced is the signal generator, a Cosmos ADCiso records analog outputs, and REW running on a MacBook Air is the software that does the work.M-Audio quote between -94dB and -86dB THD+N (A weighted) for the various inputs, which is wildly optimistic. Noise alone is -93dBFS(A) a minimum gain, which limits us to 14.5bits of resolution out of the gate. After sweeping them all to find the optimal scenario I was able to get -87dBFS(A) from the right TRS input at 1.2V/+4dBu, but it was at a -9dBFS signal level so the SNR was only -78dB. You can increase the level but distortion goes up, or increase the gain but noise goes up. Here are the sweeps at mainly zero gain, which show the domination of noise until we get into a narrow sweet spot, then followed by a rapid increase in distortion.
Here's the 1kHz FFT for input 2 at the best settings I could achieve.
There are some strange wobbles in the frequency response on all inputs - only +-0.1dB at 2kHz-8kHz, but then getting bigger and leading to a -2dB drop at 20KHz:
This odd behaviour also shows up in the multitone test:
Overall the ADC performance is disappointing.
Performance as a DAC
The headphone output driven from USB is as expected for the price - it's acceptable but no better than that, being almost entirely noise dominated. We can probably say it meets the 60mV spec at a gain of 7 into 30ohms.The RCA output gets to 750mV/0dBU so it meets its spec for output voltage but is noisy:
Performance of analog in/out is questionable
The M-Track Solo is almost unusable for direct monitoring. Switching the monitoring to "Direct" leads to results that I needed to check multiple times across two units. RCA output drops to 250mV best case but with no input headroom, and headphone out power is less than 5mW. This happened on both units so it's not a one off result. This was reflected in my experience when I tried to use it as an interface for my bass guitar, going direct from guitar->instrument in on the Solo->RCA out->bass amp it was unusably noisy. Switching to a Focusrite 2i2 solved all those issues.Conclusion
As a digital in/out interface it is just about acceptable for the price. Do not try to use it for direct analog in/out though.
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