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The FiiO M21 is the next step up from FiiO’s entry-level Digital Audio Player (DAP), the JM21, which I reviewed earlier this year. I really like the JM21, and after a couple of software updates, it has turned into an extremely versatile and competent DAP, which makes me wonder in which ways the M21 can outdo it and offer more value.

Well, one of those ways is to offer a Desktop Mode that unlocks 950mW per channel for the Balanced output, which rivals DAPs costing twice as much. At $329 USD, this isn’t your typical mid-range portable player. It was also designed with a unique case in mind that resembles a cassette player, as the M21 has various visualizations (which include cassette tape animations that resemble those of Sony’s Walkman DAPs). I did not buy the cassette-style case, but I will still cover the visualizations in my review.

The FiiO M21 also uses some of the most modern internal hardware, such as a Snapdragon 680 SOC and 4GB of RAM, all running on a custom version of Android 13. What really matters, though, is how this DAP performs, sounds, and if any corners were cut in making this the cheapest mid-range DAP. Let’s get into the review and see what’s going on.

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• FiiO M21
• Pre-installed screen protector
• Silicone case
• USB-C to USB-C cable
• Manual

The packaging of the FiiO M21 is minimal and no-nonsense. It comes pre-applied with a tempered glass screen protector, which most companies are doing now, but not to the quality of this one. It also comes with a silicone protective case, which is sturdy and feels soft to the touch. Definitely a step above what was included with the JM21.

You also get a USB-A to USB-C cable rated for USB 3.0 speeds, which is nice to see and makes this cable more multi-purpose than a standard USB 2.0 cable.

The FiiO M21 feels substantial the moment you pick it up. FiiO chose an aluminum alloy body construction that immediately signals this isn’t another plastic music player. The screwless design creates clean lines, while the choice between titanium gold and dark blue with gold accents gives you options that actually look different from the usual black slab approach. I purchased the dark blue version, as you can see.

The frosted glass back panel is very well done and serves not only as an aesthetic choice but as a practical one, as it slightly improves the grip when you are holding the player. More importantly, fingerprints don’t stick around like they do on glossy surfaces, which becomes really noticeable during daily use.

The beveled edges make holding it very comfortable, given the device’s thickness, as at 193g and 17mm thick, the M21 has some heft to it. This falls somewhere between ultraportable and desktop replacement, which means it is pocketable for most people, but you’ll know it’s there (like older smartphone users may remember).

The player itself feels like it is built superbly well, and to me, the dark blue colorway with gold buttons looks understated yet seriously elegant. Easily one of the best-looking DAPs I have in my collection. My one complaint, though, is that the paint seems to chip a little easier than I think it should. I have one corner where the aluminum body is showing under the blue color. I may have bumped the device against something, I don’t remember, but it’s something to be aware of.

FiiO went with a 4.7-inch IPS display running at a resolution of 750 × 1334. While that might sound modest compared to your phone, the bezel-less design makes good use of the available space. The fully laminated construction eliminates the air gap you’d find in cheaper players, resulting in better contrast and viewing angles. It gets reasonably bright, but you may still strain to see the display under direct sunlight. It’s nowhere near as dim as, say, the HiBy R4’s display.

FiiO distributed the controls logically around the perimeter. The very top edge houses both 3.5mm SE and 4.4mm balanced outputs, though I much prefer bottom-facing outputs (you can change the display orientation, though). The left side gets crowded with the power button, volume controls, a multifunction button, a desktop mode switch, and a hold switch, so it takes some getting used to, but everything has good tactile feedback.

Playback controls on the right side work well for single-handed operation, with the button order being previous track, play/pause, and next track. The dual USB-C ports on the bottom enable the M21’s desktop functionality, though having two similar-looking ports means you’ll occasionally plug into the wrong one initially. Here we also find the microSD slot, which supports cards up to 2TB, which should handle even the most extensive FLAC collections.

FiiO chose the Qualcomm Snapdragon 680 processor built on 6nm process technology for good reason. This octa-core chip runs up to 2.4 GHz, and paired with 4GB of LPDDR4x RAM and 64GB of internal storage, it handles Android 13 without the usual DAP sluggishness. The clean Android 13 implementation means you can actually multitask between music playback and streaming apps without any stuttering. FiiO also bypasses Android’s built-in audio resampling so that you have bit-perfect audio with every app and output being used.

The default launcher is very minimalistic. There is no app drawer, so all installed apps will appear on the home screen. This annoyed me at first, but really, I don’t install much on my DAPs, so the clutter turned out to be less than I thought it would. You can still create folders to group apps, and even have multiple pages to work with. You get access to the Play Store, as well as an Application app that seems to be curated apps selected by FiiO.

Otherwise, this is the Android you know and are used to, with the pull-down notification shade, the same essentials Settings menu, as well as the Play Store for installing apps. FiiO has added their own settings too, such as dedicated Audio section to house the various settings, as well as a Global section where you can adjust things like the navigation type (Gesture, 2-button, or 3-button), the Tape mode themes, setting the function of the Multifunction button, HOLD switch settings, enabling double tap to wake, and much more. Below are screenshots of all the major functions:

Wireless connectivity includes WiFi 5 support for 2.4gHz and 5GHz bands. My M21 connected to my access point with a speed of 433mbps, which is perfectly reasonable for a DAP. The range and connectivity are also very good, and I had no issues using the device around my apartment (which only has one access point) to stream music from media streaming services, as well as from my media server over my network.

The M21 has Bluetooth 5.0 with support for the following codecs: SBC, AAC, aptX, aptX HD, LDAC, and LHDC. What’s particularly useful is that the M21 can both transmit and receive Bluetooth audio, so it works as either a source or Bluetooth DAC depending on your needs. Receiving Bluetooth audio is limited to the SBC, AAC, and LDAC codecs.

In the Audio settings, FiiO includes an option to manually select not only the preferred codec you wish to use, but also allows you to manually select the audio quality modes for both LDAC and LHDC. I really appreciated this on the JM21, so it’s nice to see that FiiO is continuing this here on the M21.

Actual Bluetooth performance has been flawless for me. That includes LDAC’s Optimized for Audio Quality (990kbps/909kbps) and LHDC’s Optimized for Audio Quality (900kbps) modes. I encountered no stuttering, dropouts, or noise, even in busy situations like a coffee shop or just walking around outside with some TWS earbuds connected. The M21 joins the JM21 as one of the best-performing Bluetooth devices I have tested so far.

The 4000mAh battery provides respectable listening time, though your mileage will vary based on output choice:

• Single-ended (3.5mm): Up to 15 hours
• Balanced (4.4mm): Around 12.5 hours
• Real-world testing showed 14.5 hours single-ended, 12 hours balanced, and 25+ hours with Bluetooth.

The USB-C charging with 20W PD3.0 support fills the battery in about 1.5 hours, which was accurate in my testing. Since there are two USB-C connections, you might be wondering if it matters which one you use. When the Desktop Mode switch is set to Off, either port will charge the M21. When it is switched to on, only the port labeled “USB 3.0” will charge the M21.

FiiO includes various battery-related options, including being able to limit the charge to whatever you want, which is a nice feature that you can use to preserve the lifespan of the battery.

Like any other DAP that supports external storage, if you already have a microSD card full of music, you should already be good to go. I do find the absolute best and easiest experience is to use the device to format the card, then move your music, playlists, etc, onto the card, but in reality, it shouldn’t matter. I used both freshly formatted cards and existing ones that I’ve tested in non-Android and Android DAPs, and they all worked without issue. Android is less picky about where files are on the card since you are usually able to manually select the location to scan for your music.

Ideally, though, you’ll have a folder called “Music”, with all your files there. You can connect the FiiO M21 to your Windows PC, and it will appear as an external storage device, which allows you to access both the device’s internal storage as well as the inserted microSD card. This is one way you can copy files. Unfortunately, it can be unreliable at times, specifically when trying to access the microSD card this way. For the best experience, I recommend using a microSD to USB adapter to copy your files, as it will copy the files much faster than the protocol that is used when connecting to the M21 (or any DAP for that matter).

Once done, all you need to do is open your preferred music player app, scan for music in the location you put your music, and then you’re good to go! If you plan on using the built-in FiiO Music app, importing playlists is an utterly terrible experience. The FiiO Music app itself is sub-par compared to the likes of USB Audio Player Pro (UAPP) and Poweramp, but if you choose to use it, this is how you import playlists.

Save your playlists as .m3u8 files, and make sure the paths are relative, not absolute. Next, connect the M21 to your computer and navigate to the folder “\Internal shared storage\Android\data\com.fiio.music\files\playlist” and copy the playlist files there. Then, in FiiO Music, navigate to the playlist section, press the three dots on the top right, and select “Import M3U playlists”. If everything is set properly, your playlists will get imported.

Also, note that you can use a Mac to do this as well. FiiO provides a download on their site for the Mac version of the Android File Transfer app. It works, most of the time, but it can have stability issues.

I could go on more here about how I set up music and playlists on my DAPs, so if that’s something you’d like to read or even see in a video, leave a comment at the end of this review!

The boot time of the FiiO M21 is around 35 seconds, making the M21 practical for quick listening sessions. It also has good standby time performance, but I opted to set the player to turn off after 6 hours of not being used. The size and weight of the M21 mean it is like using a thicker smartphone, so portability is actually very good overall, though some might still prefer something slimmer for an everyday carry (the JM21 is better in this regard).

The FiiO M21’s interface is smooth and generally lag-free. I think we can all accept that you will not get iPhone-level optimization and performance with a DAP (yes, even the $500+ DAPs) since the majority of the processing power and battery optimizations are geared towards making sure sound quality and power delivery is optimal. App performance is still very good, though, with most apps performing the same as on my Samsung Galaxy Fold 7. I did run into some issues, such as with the Sennheiser Smart Control Plus app. It will install from the Google Play store, but it crashes when launching it. And the Tozo app that I wanted to use to test out the Golden X1 earbuds simply says it is not available to install on my device. This is somewhat expected behaviour for Android DAPs, though, as the OS is customized and optimized.

I want to give special attention to a very overlooked feature of most DAPs: the HOLD switch. I am very appreciative of FiiO for including a physical hold switch on the M21, as I use it all the time when walking or travelling with it. I’ve been spoiled by the Sony DAPs, and, for me, it is almost an essential feature for a DAP as it prevents any accidental button presses while you have the DAP in your pocket or in a bag.

FiiO’s built-in music player, FiiO Music, does an adequate job of playing music, and it’s perfectly functional with a decent amount of features. I personally use UAPP (USB Audio Player Pro) as I really like the interface and customization options, but the beautiful thing about using an Android DAP is that you can use any music player you want. Here are some screenshots of FiiO Music’s interface and its settings, and one of UAPP for comparison:

In terms of practical usability, there isn’t much else to say about the FiiO M21. It works and performs very well as a digital audio player, and there are no real deal breakers or gotchas that I have found. After the last firmware update, it feels like a very refined device.

Global EQ

The M21 has a global 10-band parametric equalizer that works across all apps and outputs. Whether you’re using FiiO Music or streaming from Tidal, the EQ settings apply consistently. You also get adjustable gain levels, multiple digital filters, and channel balance controls. It’s the kind of control that lets you fine-tune the sound to your exact preferences.

USB DAC/Operating Modes

FiiO gives you five distinct modes accessible from the top drop-down menu or Settings app. Android Mode gives you full access to everything on the device.

Pure Music Mode strips everything down to just the FiiO Music app for optimized performance. The difference isn’t night and day, but audiophiles will appreciate being able to focus on just the music player.

USB DAC Mode converts the M21 into an external sound card, while AirPlay Mode handles wireless streaming from Apple devices. Bluetooth Receive Mode lets the M21 function as a wireless DAC for your phone or other sources.

Desktop Mode + Super High Gain

This mode, when enabled via the “D. Mode” switch on the left side of the device, allows you to power the M21 using purely external power. To do this, you need to connect a USB-C cable to the “Power In” USB-C port on the bottom of the device. When active, you’ll see an icon beside the time on the home screen that is a D with a lightning bolt. You can freely disconnect the device from power as it won’t shut it down, which is nice. Once you connect the player in this way, you also unlock the “Super High Gain” mode to give you even more output power. A message will appear on the screen when this happens.

Taking a step back for a moment, I really love that FiiO includes this feature. It allows you to treat your DAP as a desktop DAC/Amp, either by itself or by connecting it to a computer or other device, and not have to worry about wearing out the M21’s battery. In a world where battery replacements are an afterthought, this function really helps preserve them. It also worked flawlessly in the 2 or so months I have been using the M21. 

The FiiO M21 features a two-stage amplification approach. The first stage handles voltage amplification while the second manages current expansion. Two OPA1692 op-amps handle voltage gain, with two SGM8262-2 op-amps managing current delivery.

Desktop Mode with Super High Gain activated pushes 950mW per channel into 32Ω loads through the balanced 4.4mm output. Even the 3.5mm single-ended output delivers 405mW per channel at 32Ω, which is more than adequate for most headphones.

I tested the M21 with various gear and found it pairs exceptionally well across different impedance ranges. Sensitive IEMs stayed quiet with virtually no background hiss. Switching to Super High Gain and Desktop Mode provided more than enough power for demanding planar magnetic headphones (like the HIFIMAN Edition XV and Audeze LCD-2), letting them reach their full potential.

Four Cirrus Logic CS43198 DAC chips work in a matrix arrangement to create an eight-channel fully differential output design. This is supposed to reduce interference and enhance dynamics. This also includes a high-precision impedance matching network for both headphone outputs to further ensure proper sound quality and output power.

If you’ve read my previous DAP reviews, then you know I don’t necessarily believe that there are distinct and meaningful differences in the sound quality between most DAPs. There are so many factors that affect the subjective observations of audio quality that it can be hard to tell what is really affecting the sound you are hearing.

With that being said, what I can say is that the M21’s sound quality is excellent. It presents a very clean audio output with no background noise, hiss, or static interference present. Even when using the 64 Audio Solo IEM, the M21 gives a very black background that is super clean, allowing you to hear what the headphone or IEM is supposed to sound like.

One interesting thing, though, is, when using the NOS (non-oversampling) filter, there can be a distinct popping or clicking sound at the beginning of each track, which is more easily heard with sensitive IEMs. Switching to another filter solves this issue, so there is something to the implementation of the NOS filter that FiiO needs to solve.

Otherwise, music simply sounds wonderful, with the main limiting factor being the IEM or headphone you are using.

The FiiO M21 has spent the last 2 months as my daily driver, and it’s become clear this player occupies a special place in FiiO’s lineup. At $329, you’re getting what feels like 90% of a flagship DAP’s performance without the flagship price tag. it even made me stop using my Sony NW-WM1AM2 for a while, which is a DAP that I love to use and costs roughly 4 times as much as the M21.

The Desktop Mode really is the game-changer here that differentiates the M21 from other DAPs in its price range. The 950mW per channel output transforms the M21. As well, the battery bypass aspect of it is just smart engineering. Why wear down your battery when you’re sitting at a desk?

Build quality feels right for the price, maybe even slightly better given how nice it looks and feels to use. The sound quality, as well, is simply outstanding, minus the issue with the NOS filter.

If you’re coming from budget players or smartphone audio, the M21 will be a revelation. Even seasoned audiophiles might be surprised at how close this comes to players costing substantially more. The Android implementation is clean, battery life is solid, the global EQ works well, and you have fully bit-perfect audio with every app and output.

For anyone looking at their first serious DAP or wanting to upgrade without spending flagship money, the M21 makes a strong case for itself. It’s the kind of product that delivers on its promises while leaving you feeling good about the purchase price. I have no problem recommending the FiiO M21 to most portable audio enthusiasts. It hits that sweet spot where performance, features, and value all come together nicely.

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