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Sigma 300 (ADAU145x) Slew Volume Rates

     Slew volume controls can filter noisy control inputs and minimize clicks.  Often the desired slew rate can be found by experiment.  However, in some applications it would help to know the actual slew rate a given setting yields.  For example, the ADAU1701's slew rates are described at

    The -1452's slew volume controls are different (and more versatile) than those of older SogmaDSPs,  There's separate rise and fall settings, each with several curves to choose from.  The "RC" curve setting shown here provides slewing similar to that of the older slew volume blocks, thus the slew rates can be measured the same way (see the post cited above).  Although this RC curve is exponential in nature (it follows the RC characteristic that includes the term e^(-t/RC), the -1452 slew block also offers a separate exponential choice. Testing the -1452's RC slewing this way results in the table below.  Slew times are given as a time constant as well as the dB/s rate often specified for SigmaDSP dynamics processors.

The Sigma 300's Exponential slewing operates in ways both similar to, and different from, the RC slewing.  The post at Sigma 300 (ADAU145x) Exponential Slewing describes the differences.

    Linear slew settings yield these 10 -- 90 % rise and fall times.  If you prefer 0 -- 100 % times, multiply these times by 1.25..

  • FormerMember
on Feb 22, 2021 3:53 PM

Dear Bob,

Is there any formula to derive time in milliseconds from the slew rate ? There does not seem to be any fixed pattern or differences between consecutive slew rates and their corresponding time in ms

Also how is amplitude reduced or increased (by a factor of what) for say each setting of the slew rate value



  • Hello All,

    I think it is time to post the details of the hardware slew engine in the Sigma300/350 processors. 

    This is what I have for information.

    Dave T


  • Reply Children
    • FormerMember
    on Feb 24, 2021 7:08 AM in reply to DaveThib

    Thanks much Dave 

    Just two more info 

    1.what is that [3:0] in your equation .

    2. Say if I set the decay to a value of 8 in the Slew ext block then from the equation for linear ramp I get a value like 0.65536

    What is it's equivalent 8.24 value ?

    Will 0.65536 be added or subtracted to each sample of my input .