I have been building a Carnatic practice app for the last 8 years (tanpura, tala, pitch check, singing evaluation, raga identification). Before I started, I thought ragas would be the difficult part. It turned out Sa was.
You all know this already: Sa is not a fixed pitch. Everyone sings at their own, 2 kattai, 5 kattai, somewhere in between, and everything else is counted from it. For an app this means a pitch in Hz is useless until it knows your Sa. Get Sa wrong and every swara after it is wrong, and the raga guess goes completely off.
A few things that kept tripping it up:
**Pa looks like Sa.** Only Sa and Pa are held steady, everything else has gamakas. So a steady note the singer keeps coming back to could be either one. Take Pa as Sa and you still get a valid raga, just a different one. Todi and Mukhari got mixed up this way in my tests.
**No Pa? Then Ma.** In Vasantha or Hindolam, Ma becomes the decoy. Treat Ma as Sa and the real Sa above it looks like a Pa.
**The tanpura doesn't settle it.** The Pa string is as loud as the Sa strings. And a Ma-tuned tanpura on C gives exactly the same two notes (C and F) as a Pa-tuned tanpura on F.
**Graha bhedam.** The same five notes are Mohanam, Madhyamavati, Hindolam, Suddha Saveri or Suddha Dhanyasi depending on where Sa is. So Sa and raga have to be found together, not one after the other.
This week I played TN Seshagopalan's Manji padam (Mohanavalli) to the app and it said Revati. That is exactly what Manji's notes look like if you take Pa as Sa. (It doesn't know Manji yet either, but that's another story.)
**Octave, and practice vs concert.** A padam sits low, so even the octave guess goes wrong. And a student practising on a phone gives you 15 seconds, no tanpura, and a Sa that slowly drifts.
The funny part is that any rasika can walk in during an alapana and know where Sa is in a few seconds.
So my question to you: **when there's no tanpura, how do you find Sa?** Is it the phrases, where the singer comes to rest, the raga itself? And teachers here, how do you teach a student to hear it?
I wrote a longer version with more diagrams here: https://medium.com/@madhurrajn/identifying-sa-digitally-is-harder-than-i-thought-630a54909694. Full disclosure, I'm the one building the app (Carnatic Tanpura, Tala & Pitch), it will be on Google Play soon. If you have recordings where Sa is tricky to find and you're okay sharing them, I would love to hear them.
