Dear Member (sikhphilosophy)
Tann in Hindustani classical music is not equivalent to Tone in english. Taan is a combination of Swaras of the Raga which are sung in a particular way, it is to added depth and beauty to the Raga being sung.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/jap-ji-sahib/350-japji-sahib-pauri-3-a.html
With Love and Respect for all.
Amarpal