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Buying Time for a Seamless Switch

Hybrid radio comes with its own set of technical considerations

The author is product manager for automotive audio at Fraunhofer IIS.

Sebastian Scharrer

Advancements in technology enable a variety of new platforms for consumers to enjoy audio in their cars. Despite the plethora of programs and podcasts available online, broadcast radio remains highly preferred for local programming, news and information.

In fact, according to Pew Research, traditional terrestrial radio continues to be the most common form of in-car listening, as compared to online platforms. The well-known challenge, of course, is to maintain audio quality as a driver moves away from a local station’s broadcast area and signal strength gradually weakens.

Hybrid radio combines broadcast transmission with an accompanying web stream, but it’s not as easy as simply switching between the two transmission channels based on signal strength.

Delays between the two sources are common, such as the typical lag from a web stream that can range from a few seconds to a half-minute or more. Making matters worse, delay times are not consistent between radio stations. Without any intelligent handling, a simple switch from broadcast to web stream will result in content that is either lost or repeated. Such delays can negatively impact listener enjoyment.

Now, innovation in the way users receive radio transmissions are increasingly available. Through the growing adoption of hybrid radio, automotive radio manufacturers are focusing on delivering an engaging and seamless listening experience, even when radio signal strength declines due to distance.


Fraunhofer IIS, developers of advanced audio technologies, now offers Sonamic TimeScaling, a technology to synchronize both signals to produce a precise transition.

The Sonamic TimeScaling technology works by enabling the radio platform to anticipate that the radio signal may soon be interrupted. This is possible because the technology is designed to recognize weakening signal strength. When this happens, Sonamic TimeScaling starts to calculate the existing offset to the web stream. Once the offset is estimated, the next step is to decelerate the signal that is ahead of the other, which continuously reduces the delay until both signals are synchronized.

Listening tests prove that this compensation process is imperceptible. While driving, a 3-percent deceleration of the audio signal is not recognized. For most listeners, 5 percent is still tolerable, though when enjoying a favorite song, for example, the playback speed difference can be recognized. The technology allows the platform to retain the transmission instead of losing the audio signal or producing an irritating repetition or signal drop-out. Most stations come up with delays between DAB+/FM and IP streams of around five to 10 seconds. Compensating this delay with 5 percent means that the process will sync both signals within two to three minutes.

The process also works in reverse, enabling the radio to switch back to analog broadcast when signal strength is restored, which also keeps mobile data usage to a minimum. Again, this is a transition inaudible to the listener and accomplished without loss of content or duplication. The pitch of the original transmission is also preserved, resulting in no audible degradation of audio quality.

In today’s evolving media world, consumers have come to expect an uninterrupted audio experience across multiple media platforms. The automotive industry is responding with fully integrated, multichannel playback systems tailored to the manufacturer’s specific vehicle. This presents new opportunities to take the in-car listening experience to the next level. New intelligent audio processing technologies such as Fraunhofer’s Sonamic TimeScaling increase this potential, seamlessly delivering an uninterrupted in-car audio experience for consumers.

The accompanying graphic illustrates this process. It depicts a radio station’s two broadcasting methods: radio signal and web stream. The offset between the two signals is marked in light blue.

The green lines represent an area where a radio signal can be received. The height of those lines indicates that the reception quality varies by location — sometimes better, sometimes worse.

A car driving from left to right will, at some point, leave the transmission area.

Reception diminishes and the listener can no longer hear the broadcast at the same level of quality, if at all.

The red arrow indicates which playback stream the listeners are enjoying.

At some point, the main unit establishes a connection to the Internet, and identifies the right web stream for the broadcaster. Before reconciling the offset, it first determines how big the delay is between the two sources.

This intelligent process does not change the audio signal in any perceivable way. Instead, it retains the original pitch of the transmission.

The gray lines represent the original signal and the green lines represent the decelerated signal parts. The growing distances between the grey and green lines depict the deceleration generated.

This gradually reduces the delay until both sources are in sync.

Once they have been synchronized, the radio signal continues at its original speed.

From this point on, both signals are synchronized with each other, so that the system can switch from radio to web stream at any time.

Independent of the growing importance of streaming services the necessity of broadcast will remain. Technologies such as Sonamic Timescaling combine the advantages of both worlds to enlarge the transmission area tremendously. Due to its physical nature, over the air transmission, unfortunately, has some limits of reaching listeners while traveling across the country. The benefit of this hybrid approach is data transmission volume will been saved, for the listener as well as for the broadcaster.

With advancements in technology, such as Sonamic TimeScaling and more efficient audio codecs, high-quality audio is delivered to listeners even when outside the OTA transmission area.