Subbarao, who was the finance secretary from April 2007 to September 2008, is a key witness in the case in which former Telecom minister A Raja and others are facing trial.
During the recording of his statement, Subbarao told the court he had written a letter on November 22, 2007 to the then Telecom secretary D S Mathur in which he had questioned the spectrum fee of around R1,600 crore for pan India licence.
He said that he had also questioned as to how the spectrum fee of R1,600 crore, which was fixed in 2001, could be applied in 2007.
I also questioned how the rate of R1,600 crore, determined in as far as back in 2001, could be applied for licences given in 2007..., he told special CBI judge OP Saini.
CBI prosecutor A K Singh also showed various files and notes of various departments concerned, including that of department of telecom and ministry of finance, to Subbarao during the recording of his statement which is likely to continue throughout the day.
Till November 11, the court had recorded statements of 77 CBI witnesses in the case in which Raja is the key accused.