In the radio industry, a song’s popularity is measured by the demand for the song based on the volume of requests from listeners and sales. The Top 40 is one of the music metrics that tracks the most popular songs within a current week, month or year. Top 40 playback became a dominant radio format during the 1960’s and was persisted until the 1980’s.
You may be wondering how Top 40 works: what is the process, how does a song make it to the Top 40? I will try to explain it further. Each week, the 100 most popular songs are put into a chart by Billboard. The Billboard chart is based on a national sample of top radio airplay and music sales. The Top 40 songs are then extracted from Billboard’s Hot 100 chart.
Airplay is the first process in determining the songs to be included in the Top 40. Broadcast Data Systems (BDS), run by Neilsen, keeps track of the airplay. BDS uses a certain technology called digital pattern-recognition to capture songs that are being played on radio stations and music channels all over the US and Canada. This recognition process is run 24/7 and captures over 100 million songs annually; the data gathered is then used by Billboard in compiling weekly charts.
The second process used in determining the Top 40 songs is monitoring the sales of albums in music stores. To track sales, Billboard then uses SoundScan, another technology developed by Neilsen that keeps track of record sales all over the US and Canada. When we purchase an album, sales data from the barcode is passed to SoundScan; the stored data is compiled and published weekly.
The methodology of Billboard in weighting the compiled data has changed over time. In the past, they were using 90% airplay and 10% sales to determine the top songs. Now, they use 80% airplay and 20% sales because of shifting trends in how many people listen to radio versus how many people actually purchase singles.