A portable DAC is very much a thing now. Not surprisingly, because even the cheaper ones offer a lot more breathing room than the DACs built into smartphones.
Whether a portable DAC is a worthwhile investment? Perhaps surprisingly, this is a question that cannot be answered very directly. Of course: if you have a basic smartphone, the thing usually provides an immediate and clearly audible improvement in quality. With more expensive midrange and high-end models, the quality gain is often quite a bit less or simply not audible. At least, if you directly compare it to an increasingly scarce headphone output on your device.
That is one of the reasons to justify a portable DAC under any circumstances: you can use wired headphones again! If this is your specific concern, you don’t have to go for the most expensive model. In that case, look mainly at ease of use and sturdiness. Some portable DACs sound great, but have a very fragile looking cord for example. DACs that you plug directly – so without a cable – into your smartphone can be a solution. But remember that these things do not always fit through a used protective case. And possibly exert a lot of force on a USB-C or micro-USB connector.
A popular device like an iPhone still only converts 16 bit/24 (or 48) kHz. All music from the iTunes Store is recorded in a compressed AAC format with 16-bit resolution (Apple’s streaming service may get more breathing room but at the time of writing is still doing it with lossless 16-bit music). Streaming services like Spotify work with 16-bit compressed streams by default. With Tidal and Qobuz, you have to pay extra to access hi-res streams. If you do, then a better quality portable DAC is a great choice.
On-the-go hi-res streaming makes sense?
However, if you are only making this purchase for the daily trip to and from work or study, then you may be more practical with a good pair of wireless headphones. In the busy noise of public transport, the finesse of the better DAC is often less well heard or not heard at all. It is also true that your mobile internet subscription may not be able to cope with the data traffic of lossless hires streams. Then using a lossy stream while on the road is the most obvious and an economical option.
Furthermore, the portable DACs actually come into their own in a living or quiet study. But whether you will sit there with headphones on? Fortunately, most ‘better’ portable DACs also perform well when connected to a hi-fi system. In conclusion: yes, the purchase of a portable DAC is useful. But only if you realize when it ‘performs’ optimally and you enjoy it most.