Audirect's Whistle sounds great. I mean I love the sound of its name. And it sounds good. From an audio perspective, it is more than worth its 99$ price tag. It gets louder than an iPhone (even approaching high-end DAP territory), keeps THD and IMD to inaudible levels, and does so with amazing unloaded performance. Even loaded it does remarkably, again approaching high-end DAP territory.
Below you'll find charts comparing it to both an iPhone SE and other Lightning dongle DACs.
Source: Audirect Whistle DSD DAC
ADC: Lynx Studio HILO LT-TB
Computer: 2012 27" iMac
Cables: 1,5m Hosa Pro 3,5mm stereo to dual 3-pin XLR (around 8$)
NL - no load
SM2 - Earsonics SM2
ES7 - Audio Technica ES7
DT880 - Beyerdynamic DT880/600
24-bit VOL (Full) @+6dB - all targets
24-bit VOL (Full) @+6dB - VS iPhone SE
