FiiO M21 Specifications:
RAM | 4 GB
Internal memory (ROM) | 64 GB (approx. 52 GB usable)
Memory card slot | One microSD card, up to 2 TB
DAC | 4 × Cirrus Logic CS43198
Amplifiers | 2 × OPA1692 + 2 × SGM8262-2
Adaptive impedance | PO: 8–350 Ω / BAL: 8–350 Ω
Channel separation | L20, R20 (0.5 dB per level)
Special decoding | MQA full decoding, all in DSD
EQ | 10-band dynamic EQ (±12 dB), 8 presets, custom EQ
Connectivity:
Wi-Fi | 2.4GHz/5GHz, DLNA, AirPlay, Wi-Fi music streaming, Roon Ready
Bluetooth reception (5.0) | SBC, AAC, LDAC
Bluetooth transmission (5.0) | SBC, AAC, aptX, aptX HD, LDAC, LHDC
FiiO Link | Wi-Fi + Bluetooth control (Android); Bluetooth control (iOS)
USB DAC mode | Up to 384kHz/32bit, DSD256
USB audio | Up to 768kHz/32bit, DSD512 (DoP/D2P/Native)
Coaxial output | Up to 384kHz/24bit, DSD128 (DoP)
Physical controls on the device:
Multifunction, Volume, Play/Pause, Previous, Next
Enter and exit:
Line output standard 3.5 mm
Balanced line output standard 4.4 mm
Standard 3.5mm headphone output
Balanced headphone output standard 4.4 mm
Battery and power supply:
Charging time | Approximately 1.5 hours
Battery life | 15 h (3.5 mm SE) / 12.5 h (4.4 mm BAL) (test: MP3 44 kHz/16 bit, 32 Ω, display off, EQ off, high gain)
Audio performance:
HR 
SL 
EN