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Dynamic bass boost in a 2.1 stereo design


I am designing a 2.1 stereo system using ADAU1702 and I want to make use of the dynamic bass boost block.

My signal chain is: input -> parametric EQ -> 2-way crossover -> bass boost -> rms compressor -> output

My question is: Is it is correct to add the bass boost to the "low freq channel" after the corssover or should I add the bass boost block directly to the unprocessed signal like:

  input -> dynamic bass boost -> parametric EQ -> 2-way crossover -> rms compressor -> output

What effects, (pros/cons) will the two different ways have? Which one is to prefer?


  •      Hello SpeakerDude,

         ADI's Dynamic Bass block features built-in frequency filtering, thus it should go before the crossover.  This way it can exercise control over the sound from all your speakers.  For example, in the circuit below the crossover is at 100 Hz, while the dynamic bass is set to operate at 250 Hz and below.  When I tested this, I can hear the dynamic bass effect through both the sub and satellite speakers.


    Best regards,


  •      Hi,

         BTW -- if your sub could also use a phase control, try this:


  • Hi Bob,

    Thanks for the information!

    I wonder if there is any graphical description of the gain that is applied by the dynamic bass bost (gain vs frequency)? For example:


    Boos Freq = 45Hz

    Boost = 6dB

    Low threshold = -20

    High threshold = 0

    Compr ratio = 3

    Lowpass freq = 250Hz

    What is the applied gain curve (gain vs freq) for signal levels between low and high threshold? How does the curve look for frequencies above and below the bosst frequency (45Hz)?

    Best regards


  •     Hello Markus,

        Yes it would be nice if ADI provided a family of typical curves for the Dynamic Bass block.  With no fewer than seven parameters to adjust, however, that might be easier said than done.  The SigmaDSP Toolbox Wiki has seen much improvement lately, but there's still not much in the way of docs for this block.  Perhaps you could ask for some curves in a new post (which is more likely to get someone's attention than here in this old thread).

        I got curious and attempted to plot some curves myself, first by running white noise through the Dynamic Bass block and out to my laptop, to record and FFT the result. I could not get audio into my laptop via its own sound card and didn't have a USB interface handy, so I drew up the circuit shown below instead.  The basic idea is to run a frequency sweep through the block under test, then have an envelope follower measure the output for viewing on a Real-Time Display.  Unlike other times I've done this, the version shown below presents a log-log (dB vs. log frequency) graph.

        Interpolator 1 produces an exponential function to drive the VCO, resulting in a 10 -- 20 -- 50 -- 100....500 Hz horizontal axis on the graph.  Interpolator 2 calibrates the vertical axis in dB, it's helped along by the square root block preceding it (otherwise its low-end resolution would be even worse than it is).  I tested this contraption with various "normal" filters to make sure it works.  Then with the Dynamic Bass block set the way you specified, here's what I measured:

        At zero dB ("full scale" or 1.0 peak level), as expected the block does not boost.  Interestingly, it cuts bass at frequencies below the 45 Hz setting.  This surprised me so I performed a listening test and sure enough, I did hear it cut the bass.  I guess the idea is that you set the block for the lowest frequency you plan to reproduce, and let it attenuate the stuff below that to protect your woofer from shaking apart.

            Reducing the level to -40 dB, we now see the 6 dB bass boost at 45 Hz, with more or less the same cut at lower frequency.  Clearly, it will take some experimenting to find the response you need (that's what the wiki says also, to its credit).  I attached the project which runs on the ADAU1701MINIZ board, in case you wish to experiment with some more curves.

         BTW -- while running a listening test my engineer friend came over to say, "Bob, that's oppressive bass."  Obviously, there's no accounting for taste.

         Best regards,