DECIBELS & DIGITAL PLAYOUT SYSTEMS

When we work with audio equipment, it is important to keep track of the overall levels of the audio we are working with for two reasons:

1. So that we can compare the relative levels of various sounds and recordings, in order to adjust them relative to each other; and

2. So that we can keep the audio levels at a level where the equipment’s circuitry can handle it.

In order to do this, however, it was important to develop a system of sound units which could mimic the human ear’s way of distinguishing. The units which were developed became known as the Bel and the deciBel (dB). The Bel was named after Alexander Graham Bell, the inventor of the telephone. A deciBel is one tenth of a Bel, and is the more commonly used of the two measures, as the Bel is a very large unit.

As a measure, the Bel and decibel are logarithmic. Logarithms are an arithmetic system where large numbers can be expressed as a system of smaller numbers, and where the progression of numbers is not linear in nature. (Our hearing is actually logarithmic in nature: A sound that we perceive as twice as loud is actually nearly four times as loud in absolute pressure terms, so it is easier to perceive this in relative terms. Additionally, ‘loudness’ is a very subjective quantity.)

What is important is to grasp that dB always represents a ratio of two quantities, and not a quantity itself. This can be the ratio of two powers, voltages, currents or sound intensities. Most often it is a ratio of power quantities. As we have seen, it is immaterial whether we talk about an audio signal in terms of the actual pressure wave that we hear or the change in electrical voltage that a microphone converts it into. Thus, if 0 dB is specified as some reference value then any number of dB above or below that zero reference can be used to describe a given quantity.

The standard dB term used for expressing input and output voltage is dBu. 0 dBu corresponds to a voltage of 0.775 volts. Another dB unit that is often used is the dBv, which is equivalent to the dBu. An older dB unit that is used is the dBm. 0 dBm is 1 milliwatt. dBm has no direct relationship to voltage.


The advent of computers has not only made the process of editing and manipulating audio easier, it has also made the process of storing and accessing large quantities of audio data very convenient. Where radio was once a purely ‘live’ medium, today we can select and playback a huge variety of programming with the click of a few buttons.

At its most basic, a digital playout system is a computer set up to playback audio for broadcast. Most computers are capable of playing back audio with an appropriately installed sound card and audio playback software. What distinguishes a digital playout system from other such computers is the software used to organize, sort and search through the audio stored in its hard disk – and to ‘queue’ the audio so that it plays back in a specific sequence and without a pause.

A large part of using a playout system is creating the sound files the system uses. For this, the audio must first be stored as digital audio files on the playout computer. If the original audio is on an analog medium like audio cassette or LP record, it will first have to be digitized or captured, and then transferred onto the playout system. On the other hand, if the audio is already on a digital medium like a CD, it will need to be ripped using a ripping software. Ripping is essentially a process of converting the audio from its original digital format to an audio format that is compatible with the playout software.

Most playout softwares are compatible with MP3 format files!

All the audio that will be broadcast (‘played out’) from the playout system has to be in the form of audio files on the playout computer – jingles, ads, programmes, music, teasers, everything. Since digitization may be a time consuming process, this generally means that one must have separate systems for the production work and the playout, because the playout system cannot be utilized for any other work while the broadcast is going on. If you do decide to share a single system for production and playout, remember that you must have large amounts of hard disk space and that you must plan in advance to share your time across these two functions.


Organising and managing the sound files in the playout system is the most demanding part of using the system. If sound files are not named according to a common convention and properly organized, the playout system becomes completely chaotic and it becomes impossible to find specific sound files. It is essential that everyone who uses the system knows how the sound files are organised. Since a number of people – community reporters, station manager, community volunteers – may be operating the system, this process must be set up when the system is first installed. Usually, the computer is set up with a folder where music sound files are saved, a folder for ads and jingles, a folder for finished productions such as interviews, one for sound effects and so on. Some systems already have folders for storing different items but will still rely on the user to label the item or save it in the right place.

Folder systems and file naming conventions are sometimes dependent on the specific playout software being used.

Playout systems make the presenter’s job much easier. At the same time, the station will need extra computer skills to maintain the playout system, and this can make the technical department’s work more difficult. These skills can be difficult to learn and so it is important to have a good relationship with your supplier to talk through problems as they arise.

Digital automation systems – the next step

The digital automation systems are the next higher step beyond the audio playout systems, allowing us to automate the entire task of broadcasting programmes according to a pre-decided schedule. Once specific time slots have been set for various programmes to air, and for the programmes to be interrupted at specific points by advertisements, public service announcements and programme promos, the digital automation system allows us to simply line these up for several days in advance, for the programmes to play out completely without human interference.



Naturally for this system to work to its true potential, this means having a full time team to manage and organize the audio on the system, not to mention full time teams working on generating the programming and the advertising (especially if the programming team is also producing the advertisements on behalf of the advsertisers). It also means an enormous level of coordination and cooperation between these teams in terms of getting the relevant audio ready several days in advance of the play date.


Given the scale of operation of a CR station, automation must be used with care. Extensive automation also means having a full time infotech team that can manage and maintain the computers involved at all times. This is only a viable option if your station is doing more than 8 hours of broadcasts a day.