Our ancestors, who did not have computers or synthesizers were surely tuning 22 Shrutis by hearing.
The following table will explain the procedure of tuning the 22 Shrutis purely by S:P or S:M bhava, as these are easily 'understood' by the ear. Only at 2 places, we shall have to use our sense of S:G bhava.
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Table shows procedure to tune 22 Shrutis on 22 strings or 22 reeds 'by the Ear'