Sending audio from the field back to the studio has evolved from leased lines and RPUs to ISDN and now to IP. At the same time, the power of the handheld devices we carry has been put to good use in radio as well. There are many apps to record quality audio from the field. There are also hardware add-ons to improve the recording functions. But there's another use for that smartphone when you need to get audio back to the studio.

A typical telephone call is still the simplest method to deliver audio, and with so many people carrying phones, it's easy to connect from anywhere. But a standard phone call is limited in audio bandwidth, and is hardly comparable to the high-quality audio available through other means. Bad audio is bad radio.

So why not take advantage of the digital connection of the smartphone to deliver better audio via 3G, 4G or Wi-fi? That's what some apps now do.

Using Session Initiation Protocol (SIP), a handheld device app can communicate with another device, like an IP codec at the station. The app connects to the receiver's IP address. The EBU working group for Network Audio Contribution Over IP (N/ACIP) adopted SIP for codec interoperability and included it in the Tech 3326 standard. Devices can connect directly or through a proxy server.

The handheld apps provide a signal path with a higher bandwidth than a typical POTS telephone call. The ubiquitous G.722 encoding provides a 7kHz connection, and other encoding algorithms provide quality up to 15kHz.

Some apps can also record audio for later transmission, which adds to their flexibility.