A sruti box is a small wooden instrument that works on a system of bellows. It is similar to a harmonium and is used to provide a drone in a practice or concert in Indian classical music. Adjustable buttons are present for tuning. Nowadays even electronic sruti boxes are commonly used. It is also called sruti petti in tamil and sur peti in Hindi.

History

Before the arrival of the harmonium in India, people used either a tambura for the drone or specific pitch reference instruments like the othu nadaswaram. After the harmonium became popular people started hacking the harmonium to be used for the reference pitch. Typically one would open up the cover and use the stop of the harmonium to produce a drone.

Later the keyless version of the same was invented for the specific purpose of producing the drone sound. These also had circular wooden controls on the top and below the cover that is used to control the pitch.

The modern version however is a compact electronic device. It consists of an in built speaker and the necessary electronics to produce the drone. Almost all of these electronic instruments allow adjustments and fine-tuning. In a concert, the sruti box is miced to the mixer. Rarely does one come across a sruti box which can be directly wired into the mixer unit.