Planning for Surround

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Proper monitoring

No matter how far you decide to go with your studio conversion, it's extremely important to include proper surround monitoring in the design. Surround monitoring doesn't have to be complicated, and can simply be a consumer-style receiver with a built-in surround encoder. Install surround monitoring in the production room and the control room. The station is distributing a special product; let the announcers enjoy the surround experience. The more ears listening to the final broadcast, the more likely that problems will be prevented.

Figure 3. A full-surround production studio implementation.

The monitor installed for the production rooms should also have the ability to decode all of the major surround systems: Dolby Pro Logic, SRS Circle Surround and Neural Surround. In the near future you will also begin to see the MPEG Spatial Surround on the market for use with HD Radio. When producing a spot, listen not only to the final product through the chosen surround decoder, but also through the other decoders. The radio station may be transmitting in Neural Surround, but the listener in the car has his radio set for Dolby. You need to know what the listener will hear.

Cross-compatibility listening tests have shown that for the most part the listener will have a pleasant experience whether listening to the proper decoder or someone else's, but don't let your guard down.

Proper training for the production staff is also a must. While many production managers may have been in the business for many years, surround production will still most likely be new to them. Train them to produce elements that will capture the audience.

What about multipath?

Multipath distortion has been responsible for squashing previous attempts to improve audio separation. The varying multipath signals can cause noise and distortion in the received audio signal and can even cancel the carrier altogether. And excessive stereo separation can increase the effects of multipath. Because surround systems encode their surround information in the stereo channels, the L-R channel of the composite stereo signal may increase in level and cause issues with multipath. Tests have shown that, in most cases, the encoded audio has little, if any, affect on multipath. If you suspect an increase in multipath, view the L-R channel on a scope with and without the surround encoding to see if there is a major change in the L-R signal. You may actually find high L-R energy in the non-encoded signal to start with. Don't assume the surround is the cause of the problem.

Don't forget multicasting

Multicasting tops the list of the benefits that HD Radio has to offer. If it were to come down to a choice of broadcasting an HD2 channel or broadcasting in surround, the HD2 choice would win. For this reason the surround proponents have been challenged with making their systems work well even at reduced data bit rates. Early testing at rates of 64kb/s and below are showing promising and impressive results. When building new multicast stations don't forget to allow for surround, even if it's not used at first.

The future of radio is not grim, but can be rather exciting if we continue to move forward with new HD Radio channels, new programming formats, new digital features and new improvements to audio such as surround sound. When remodeling a facility, keep all of the new technologies in mind during the design stages so that you will be prepared when asked to turn on a new feature. This will help you win the game and become the hero.

Fluker is the director of engineering for Cox Radio, Orlando.

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