Units in slew external volume control?

Hello everybody, sorry if this question has already been answered, I haven't been able to find it. Could anybody please let me know what are the units of numbers which we put in a slew block to determine slew time? Are those samples? Most probably not. Please help!

  • 0
    •  Super User 
    on Sep 8, 2014 1:53 AM

         Hello Skfir,

         I couldn't find any slew-volume specs either, so I set out to measure it.  In the circuit below, a square wave feeds the slew volume control. The result can be seen on the Real-Time Display as an exponential rise and fall, so we can model the Slew Volume control as a first-order "RC" with a time constant.

    The Real-Time Display, however, is inconvenient for accurate measurements.  Thus, the circuit has Stopwatch cells counting samples as the slew output rises from 0 to 0.63, and falls from 1 to 0.37 (either is one time constant).  The read-back cells are scaled to show the time constant in units of 0.05 ms, considering the 48K sample rate and the read-back's four-bit truncation (divide by 16).

         Here's the results expressed in time constant as well as the dB / s spec used elsewhere in SigmaStudio:

    • Rise and fall times were identical
    • Increasing the slew number by 1 doubles the slew time (a power-of-2 relationship)
    • The slew numbers useful in typical applications range from about 8 to 15

         Best regards,

         Bob

  • That is great as always bob! Thank you again. It would be great if the AD people added this table into the documentation - it is extremely useful. Thank you again.

  • 0
    •  Super User 
    on Oct 18, 2017 4:39 PM

         Yes documentation -- what a concept.  I'd put stuff like this in the Wiki except that it's not particularly user-friendly and besides, you don't get any points for doing that.  "What gets done is what gets rewarded," I remember hearing at an old Fred Pryor seminar.

         Best regards,

         Bob

  • Hello. I'm trying to use this block on a ADAU1467, but the attack/decay numbers only go up to 15 i.e. about 700msec - I need to go at least 10x slower than this. Is there any way to achieve this please?

  • 0
    •  Analog Employees 
    on May 3, 2021 10:04 PM in reply to dunmail

    Hello dunmail,

    The Hardware slew is setup in firmware and the variable that sets the slew time is a 4-bit variable. So 15 is the max. This is in firmware so there really is not a work-around to hack the HW slew. The trick would be to use a software slew block and control it from an external source. Let me think this one over. 

    Dave T