The sound of crickets all singing together is sometimes referred to as an orchestra. The song of most tree crickets is a sustained trill. Late summer and fall is the time when the cricket Orchestras here in Sonoma County start to tune up and fill the night with their music!
Tune into KRCB.org (104.9 FM Sonoma County) to listen for the current segment. Ear to the Wild is a short interstitial segment aired somewhat randomly throughout the day between other programs. They use shorts and postcards to fill airtime during breaks from Morning Edition and All Things Considered. Also during their music programing, as needed. Greta Mart tends to air them during her show around 4:47 or 5:47.
Check out these links for more information about crickets:
Oecanthinae.com: A male Western tree cricket singing
Britannica: Cricket
The Orthopterist's Society: Sample Songs of Crickets and Katydids