These days, many recent smartphones no longer include analogue headphone jacks. Implicitly, the idea is to favor wireless Bluetooth headphones instead. As a result, if you want to hook up your wired headphones, one would need to buy a headphone adaptor which may come with your phone (for example, Apple at the beginning included their Lightning to 3.5mm Headphone Adaptor and these days may include some Lightning EarPods).
Recently, I upgraded my phone to the Huawei P30 Pro which does not have headphone output, so I was in the market to get one of these for the phone's USB Type-C digital connector.
Many of these headphone out / DACs are inexpensive, and the adaptor I have here today - the Soditer USB Type-C Headphone Adaptor - ~US$25, is advertised as supporting hi-res playback (even up to 32/384), and is claimed to provide up to 35mW into 32Ω headphones. Let's have a look...
Opening the box, here are the contents:
There's a plastic-metal case, the adaptor itself is small, the form factor is that of a short cable approximately 5" in length from tip of the USB-C connector to the headphone plug. It should support standard microphone passthrough when connected to a TRRS headphone plug. The deep bluish metal ends and plastic cable construction feel quite good and should be reasonably robust in daily use.
And here's what it looks like connected to my phone (playing Pet Shop Boys' PopArt compilation), headphones are the 1MORE Quad Drivers.
Based on the Soditer ad, they say the DAC inside is the Realtek ALC4042 chip. I'm not able to find the datasheet on this part so I'm not sure what to expect qualitatively. All the more reason to check it out on the test bench!
What I can say is that subjectively, it sounded quite good out of the package with that set-up above connected to my phone and those 1MORE headphones. The sound was adequately loud, punchy, decent resolution. Certainly adequate for mobile listening using Android USB Audio Player PRO.
I. Oscilloscope Waveforms, Impulse Response, Digital Filter
Yes, indeed we are looking at a linear phase filter being employed. It looks like a reasonably steep filter. Let's see how the Digital Filter Composite (16/44.1) graphs look:
There's evidence of intersample overloading with the 0dBFS wideband noise. Notice the extra "hump" up at 26-27kHz which is unusual and suboptimal performance.
I found that the output impedance is rather high at 20Ω (derived off voltage drop measured across a 51Ω resistor, 1kHz signal). Based on the "1/8 Rule", frequency response may be siboptimal for headphones of <160Ω impedance.
Another finding is that paired with my Huawei P30 Pro, with a 30Ω load, I'm measuring only around 10mW peak output which is significantly less than the advertised 35mW into 32Ω. At peak volume into 30Ω, the waveform still looked clean at least without clipping. Not sure if peak output power would vary between different phones; might be worth checking.
II. RightMark ResultsWhen I plug in the DAC to my cell phone, it identifies the device as "TX 384kb Hifi Type_C Audio" and Onkyo HF Audio Player tells me the supported frequencies are 44.1/48/96/192/384kHz. Sadly, no support for 88.2kHz which is a natural one for conversion from DSD64 to PCM. Over the years, I've come across other devices like this including the Google Chromecast Audio.
Since I typically don't care much about hi-res music on my mobile devices, let's make sure 16/44.1 performance is good:
Yup. Not bad at all. 16/44.1 performance is not a high bar to jump over these days of course. The noise level is good, relatively low harmonic and intermodulation distortions - notice how the AudioQuest Cobalt performs rather poorly compared to the others.
24/96 (downsampled to 24/48 on Android phone, and using Windows 10 laptop):
As we move into the realm of "hi-res" audio reproduction, I ran into a couple of major issues with measuring the Soditer DAC/adaptor.
Fist, I noticed that the latest update to my phone prevented both Onkyo HF Player and USB Audio Player from playing native sample rates beyond 48kHz! As a result, through the phone, at best I could get was a resampled signal. Here's what I got for the 24/96 test signal sampled down to 24/48:
|Note that I've added the Oppo UDP-205 (RCA out) to the results for comparison with a high quality reference DAC, notice the low level 60Hz A/C mains hum.|
Historically, I have noticed that measuring inexpensive DACs can be a bit of a pain with RightMark - I suspect they sometimes drop samples or have poor clock accuracy throwing off test signal time markers. If too much of the signal gets clipped off, the measurement ends up being invalid. Sadly, this issue cropped up when connecting this little DAC to my Windows 10 laptop (WASAPI driver) which was the second problem I ran into. Even though I can see that indeed it can handle 96kHz and can put out a signal with ultrasonic content >24kHz, the measurements just never looked right and I could not get good readings.
Nonetheless, I can show that the frequency response is reasonably flat at 24/96kHz using a white noise signal captured over 20 seconds. The -3dB point is around 45kHz. Increasing to 192kHz does extend the frequency response up to about -3dB at 88kHz. Not bad! (I didn't bother trying 384kHz.)
As for distortions, I can still examine the 24/96 THD+N the old fashioned way at a few frequencies - 500Hz, 1kHz, 10kHz, 20kHz using REW's realtime analyzer (24/96, -3dBFS test signal). THD sits around -90dB through the audible range. 1kHz THD+N is -86dB (0.005%) - not bad as well.
Notice that in the graphs above, I took out the usual 20kHz lowpass filter that results in increased noise for THD+N with the 10kHz and 20kHz measurement. THD remains low with these higher frequencies.
I had a look at 24/192 THD(+N) as well, and results were similar to the above.
Clearly not the cleanest looking J-Test results. There's a combination of a couple obvious sideband pairs in the 16-bit test along with various low-level noise. Remember that since the device does not support any other samplerates in the 44.1kHz family, I suspect that internally, the data is being resampled to 48kHz which would add to the low-level anomalies we're seeing here. The 24-bit J-Test result (which is fed at 48kHz, and thus likely not resampled) is much cleaner.
Despite these findings, I still would not be worried about jitter being audible.
IV. SubjectiveI spent a few nights listening to this little adaptor using various headphones I have here - the 1MORE Quad Driver (rated 32Ω impedance), AKG Q701 (discontinued but similar to the AKG K702, rated 62Ω impedance), and my reference Sennheiser HD800 (300Ω impedance).
While this little DAC/headphone out is not the best headphone experience I've had, music remains enjoyable :-)! While the output power into low impedance loads is lower than advertised in my testing, the Quad Driver (sensitivity 99dB/mW) was loud enough to be uncomfortable at maximum volume still. However, the low sensitivity of the AKG Q701 (around 93dB/mW) presented more of a challenge especially with a dynamic recording such as the Telarc O Magnum Mysterium (DR13) listened to over Easter weekend. The stereo separation is good and dynamics such as the percussion off Zhao Cong's Dance In The Moon sounded excellent. The Sennheiser HD800, while higher impedance, was able to play a little louder than the Q701 and sounded good. Of course, it's a bit ridiculous pairing such headphones with an inexpensive, low-power headphone amp such as this and one would not be walking around town with such headphones on!
Remember, while as "perfectionist" audiophiles we often enjoy listening to pristine, natural sounding, high dynamic range music in our homes with low ambient noise, when you're in a car or walking around with headphones on, low dynamic range, "louder" music is often preferred as it rises above the chatter and street noises. With low power, inexpensive, DAC/headphone output devices like this, a typical DR9 album such as Childish Gambino's Awaken, My Love! sounds great when out and about. This is likely another big part of the tendency towards low-DR mastering over the years (beyond just "loudness war", louder = better rationale) as more of us listen to music on-the-go.
V. ConclusionAs you can see, for around US$25, the Soditer "Fourth Gen" USB-C headphone adaptor works but clearly isn't the fantastic hi-res DAC based on ad hype. I trust that this is no surprise since specs are exaggerated all the time. One should not be expecting performance comparable to good quality hi-res DACs at this price point, right?!
Hi-res playback using Android phones like the Huawei P30 Pro can be frustrating and I've found that the capability fluctuates depending on firmware updates; for example, the current EMUI 10.0.0 phone update recently seems to have messed this up with USB Audio Player. Nonetheless, using Windows 10 connected to my laptop, I can demonstrate that this DAC is capable of extended ultrasonic frequency response and can benefit marginally from 24-bit data. Despite the resolution limitations and high output impedance, let's remember that we are in the era of wireless Bluetooth headphones and these results are objectively better than lossy compressed technology (for some context, remember the measured results from lowest common denominator Bluetooth protocol, SBC).
USB-C to headphone adaptors are cheap these days and you can easily get both Apple and Google-branded devices that perform well based on the tests here even if they might not advertise stuff like 24/96+ samplerates like this unit. Also back in 2018, I tested the Apple Lightning to 3.5mm adaptor which performed reasonably well for 16/48 playback.
Bottom line... The Soditer USB-C to headphone adaptor works well enough for listening around town as a replacement headphone output for USB-C smartphones. It's small, light, easy to tuck away on trips, and you probably won't lose it inside the carry pouch. The adaptor appears to be well built and should be sturdy enough for prolonged daily use. I don't have an easy way to measure the power draw but I anticipate it to be very low (it gets very mildly warm after prolonged use BTW). From the perspective of high fidelity sound, yeah, one could say that it can take advantage of hi-res files, but the benefits are certainly not by a large margin.
I see that there are other versions of this kind of Realtek ALC4042-based adaptor such as this HIDIZS and this KRIPT model; likely similar performance and potentially better prices if you shop around.
Having said this, going forward, I think it's worth considering that it is in fact more interesting to measure and listen to these "cheap" DACs to see how well the "low end" advances over the years! Imagine if in 5 years we might see inexpensive devices like these performing at 20-bits resolution - now that would be fantastic advancement in high fidelity!
Generally we don't see devices like the Soditer reviewed or measured in the mainstream audiophile media as this is not where advertising dollars are derived. At this point in history, those flagship ESS ES90X8 and AKM AK4X9X DACs are already performing at levels of fidelity well beyond the limits of human perception. Other than new features added or a company messing up a design based on those DACs such that reviewers might want to steer consumers away, I suspect there's little new or interesting to be added by measuring yet another technically "perfect" converter!
Remember, about a year ago, I was able to show that in a blind test, you (audiophiles of the Internet) were able to differentiate to a statistically significant degree that a computer motherboard output sounded poor compared to other audio devices playing back standard resolution audio. Can you show me this time that using well-recorded music, as a group of audiophiles/music lovers, you're able to show preference against (or even for) samples with high harmonic distortion added - amounts that would be considered very poor for modern DACs, streamers, and amplifiers?
Get involved, send me your impressions, and we'll see in a couple weeks or so. A big thank you to those who have already submitted results! :-)
Stay safe everyone... Hope you're enjoying the music.