Data was exchanged daily via 1200, then 2400 baud modems. J-29 (2400 through 38400 baud). The signaling rate is limited to 9600 baud. The original protocol operated at 4800 baud with subsequent releases standardising on 9600 baud. Modems tended to sell at US$1 per baud. BITNET links originally ran at 9600 baud. Modems can also be classified by their symbol rate, measured in baud. The tones are sent at 31.25 baud or every 32 milliseconds. This system operated on UHF frequencies at 9,600 baud. Recording speeds offered as standard are 300 baud or 2400 baud. Such clock synchronization is used in synchronization in telecommunications and automatic baud rate detection. Eight-to-fourteen modulation as used on audio CDs has bit rate of the baud rate. FSK441 employs multi-frequency shift keying using four tones, at a data rate of 441 baud. Symbol rate, baud rate, is the number of transmitted tones per second. The protocol could go to 9,600 baud with some loss of range.