Apogee One works as an iOS mobile concert recorder

For years, fans with Sony TC-D5M recording decks slung over their shoulders followed the Grateful Dead, carefully documenting every show.

Now, the Dead are defunct and cassette tape players are history. But there is still plenty of music worth recording, and the Apogee One, combined with an iPad or iPhone, works as a modern substitute for the venerable TC-D5M deck.

Apogee makes professional recording equipment, and its One is a portable digital-to-audio converter (DAC) with unique features. While it can generally improve the quality of audio from just about any source, I found it works best as a pocket-sized studio.

Most audio these days is stored in digital format, from the MP3 tracks you find on the Internet to the CDs still gracing the virtual shelves of Amazon. To hear it, you need a DAC to change the bits to analog signals able to push the cones and membranes found in speakers. DACs are found in devices from small adapters to PCs, and they differ greatly in quality. Apogee emphasizes the high quality of its DACs.DAC to change the bits to analog signals able to push the cones and membranes found in speakers. DACs are found in devices from small adapters to PCs, and they differ greatly in quality. Apogee emphasizes the high quality of its DACs.

The One features a metal case with a rubberized base that gives the device a solid feeling. A large dial on the top also serves as a button to change input and output modes, and a microphone sits toward the front. On the front of the One are three ports, one 1/4-inch digital input for an instrument or external microphone, a Mini-USB port that connects to a Mac or iOS device, and a power port. The other end offers a headphone jack, and underneath is a compartment for two AA batteries. At 6.25 inches long and 2.25 inches wide (15.9cm by 5.7cm), the One fits into a deep pocket or bag.

Those ports allow for a lot of flexibility in uses, but Apogee keeps the control interface simple. Pushing the dial let me cycle through external mic, instrument, internal mic for inputs, or to its output mode. Turning the dial adjusted the recording or output levels, depending on the mode. Impressively, the One handles two inputs simultaneously, letting you record a digital instrument and vocals at the same time, for example.

For my first test, I plugged my iPhone 5S into the One, fired up GarageBand, and recorded a friend playing a ukulele through the One's internal microphone. LED level indicators on the One helped me set the input level, but I could also look at GarageBand to see the incoming waveform. The resulting file gave crisp and clean playback with plenty of depth. I was very pleased with the quality of the sound, partly due to the high-quality microphone in the device.

Such things as file format, which will determine quality, are up to whichever app you for recording. The One works with any app that uses the core recording features of iOS. Storage, especially when recording a live show, will be an issue. Make sure your iPhone or iPad has enough available storage.

The flexibility of the One lets you use it to improve playback quality from digital audio sources. For my second test, I plugged in my iPhone, then plugged in a set of Koss PortaPro headphones to the One's headphone output. Listening to a 320 kbps MP3 of M.I.A.'s "Matangi" album, I found no discernible difference between listening through the One and plugging the headphones directly into the iPhone. While I don't doubt the DAC in the One is of better quality than that in the iPhone, the added hardware may have eliminated any potential gains.

For my third test, I plugged the One into a home stereo system consisting of a Peachtree Decco amp paired with Kef C5 tower speakers. Using the same M.I.A. album playing from the iPhone plugged directly into the amp versus running the One inline between the iPhone and amp, I found the One created a deeper, richer sound.

Although I preferred the playback through the One on the home stereo, I did not find it a big enough difference to warrant adding the $350 (£30, AU$430) device to the system. I usually play music off of networked attached storage, controlled through a Sonos system , and using the Peachtree amp's own DAC, keeping the path as uncluttered as possible before decoding the digital signal.

After running through my various tests, I concluded that the best use of the Apogee One is mobile recording. While it may add quality to some playback situations, it is too pricey for the casual listener. Home audiophile buffs will likely not be playing audio directly from an iOS device.

However, for professional recording equipment, the price is very good. The multiple inputs and the potential for dual source recording add great flexibility. I was impressed by the quality for the internal microphone, but you can also plug in your favorite external microphone. The case feels rugged and the fact it can run on batteries makes it a good portable solution for recording shows or artists at remote locations.