The drone of a shruti box in your pocket. Thirteen valves that glow and breathe, 43 drones, ragas and chords, your own presets in a sequencer with crossfade, a voice trainer that listens, and any USB MIDI keyboard to play it all.
Thirteen valves, Sa to Sa'. Tap one and its reed sounds, beating like a real reed, breathing with the bellows.
8 tanpura tunings, 24 ragas with their aroha and avaroha, 11 chords. Every one moves with your key.
The save icon keeps whatever sounds as a CUSTOM card. Name it, rename it, delete it.
Number your cards with taps, press ▶, and they follow each other at your BPM, one fading into the next.
The box plays a note, you sing it back; a row of lights shows how close you are, to a tenth of a semitone.
AUTO walks the scale through any range of the 88 piano keys, at ±20, ±40 or ±60 %.
Plug in a USB MIDI keyboard: keys held, velocity-sensitive, every key at its own pitch, the screen following your octave.
Sa anywhere from C to B, the box from C1 to B5, a cold blue or a warm amber light, portrait or landscape.
Nothing is recorded: every reed is synthesised on the phone. One cycle of a free-reed tone, 28 harmonics with the odd ones stronger, played as two voices a cent and a half apart for the beating of a real reed. Each valve swells in and fades out so a tap never clicks, and the bellows breathe the whole box slowly. Open more valves and the level follows, so the box never shouts.
DRONES 8RAGAS 24CHORDS 11CUSTOM ∞
The drones keep the tanpura's own logic: Sa, Sa' and one tuning note, Pa as a rule, ma, Ni or Dha when the raga asks for it. The ragas, from Yaman and Bhairav to Malkauns and Charukeshi, carry their thaat, time, mood, aroha and avaroha, and their notes are marked on the valves. The chords are Western chords played as drones.
CUSTOM is yours: whatever sounds, the save icon keeps; ✎ names it.
In CUSTOM, switch on SEQ and tap your cards in the order you want: each gets a number. ▶ SEQUENCE plays them round and round, one beat each, at the BPM you set right there. XFADE lets one chord melt into the next over the time you choose, so the box changes like breath, never like a switch.
Play a note, close the box, and sing it back. The microphone opens only when every reed is silent, so it hears you and never the shruti. A row of oval lights is the tuner: the middle one is the note, flat to the left, sharp to the right, each light a tenth of a semitone.
Any class-compliant USB MIDI keyboard works; it was made with a Novation Launchkey Mini MK4 25. The phone gives it power through the cable.
No change in loudness? Your keyboard may be set to a fixed velocity in its own settings.
The keyboard we use: Novation Launchkey Mini 25 MK4, 25 mini keys, 16 pads, small and powered by the phone. About €114 on Amazon.de (October 2026). See it on Amazon.de →
The phone has one USB-C port, and the keyboard takes it. To keep the phone charging through a long kirtan or a morning practice, put a small USB-C hub with Power Delivery pass-through between them.
Aluminium body and braided cable, four USB-C ports at 10 Gbps, 100 W Power Delivery pass-through. Small enough to live in the keyboard's bag.
about €43 on Amazon.de (October 2026)
See it on Amazon.de →Any USB-C hub with PD pass-through and USB-C data ports works the same way. Check the price on more than one site before you buy: identical hubs often cost twice as much.
The free reed, a thin tongue of metal that sings when air passes it, is far older in Asia than in Europe: the Chinese sheng is named in the Shi Jing, three thousand years ago. Europe met it in the late 18th century, and by the 1840s it had become an instrument of its own.
Alexandre Débain receives a patent for the instrument and for its name, harmonium: free reeds, blown by foot treadles.
The harmonium reaches India through traders and missionaries, first in West Bengal. Indian musicians sit on the floor, so the foot pedals give way to bellows pumped by hand.
Dwarkanath Ghose founds D. Ghosh and Sons (later Dwarkin) on Lower Chitpur Road and is credited with adapting the imported instrument into the hand-pumped Indian harmonium.
Before, the drone came from the tanpura. Musicians began holding harmonium keys down for a steady Sa and Pa; then a box without keys was built for the drone alone: the shruti box, also called sur peti. A keyless harmonium, only for the drone.
G. Raj Narayan, an engineer and flautist, builds an electronic shruti box, and his electronic tanpura follows in 1979. A drone that never needs pumping.
From Indian classical practice to Irish song and the kirtan circles of the world, the shruti box holds the ground: Sa, Pa, Sa', and the voice rising over it.
A mantra is sound before it is meaning. A steady drone gives the voice a home to return to: you hear at once when you drift from Sa, and every syllable settles on the same ground. That is why the shruti box became the companion of mantra singing, kirtan and bhajan, and of the plain Sa–Pa–Sa practice that every Indian singer starts with. Its player can pump with one hand and sing at the same time; this app needs no hands at all.
Gayatri Mantra, Chant for PeaceSoulSoundSister
Mangala Mantra Chant with Shruti BoxLumira
Kirtan series, Mantras with Shruti Box DroneHarp Musica
Shruti Box demonstration with Gayatri and Maha Mantrachillbobaggins
Chanting practice with shruti box (Saraswati Mantra)Mary Isis & Pathways of Transformation
Gayatri mantra on the shruti boxPrem Adri
Free, for every singer, every chant, every morning practice.
⬇ Download the latest version APK · 1 MBAndroid 8 or newer. Free, no account, no ads, nothing collected. Your phone asks once to allow installing from your browser.
After a sound bath, a bowl waits by the door. This app is free and always will be; if it helps your practice, ring the bowl and leave a gift. It goes straight to Marko, and keeps a struggling artist making music.