ADAU1701 noise floor & dynamic range notes - diyAudio
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Old 23rd July 2015, 09:11 AM   #1
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Default ADAU1701 noise floor & dynamic range notes

Having recently plunged into using this DSP for a project after a lifetime of using analogue I am somewhat taken back by its real world performance particularly given the chips specifications. When I first ran this chip I had terrible problems with the internal level meter as displayed by SigmaStudio however using readback in hex of the peak level helps understanding of these blocks, after consulting AD it turns out the ADC has a horribly large DC offset that must be blocked using the DCB function. I used REW to generate test signals to assist in calibrating the beast!!

The internal rms meter does not show levels below -45dB so the method I used was the peak capture block and noting the levels in hex, these can then be converted to decimal and ratio's turned directly into dB. Using this method and checking the output for distortion it was possible to establish the saturation signal level of the ADC and this is about +1dB and peak 8,0,0

With the inputs shorted the peak became 0,0,20 hex giving a noise floor of -84dB........this is way higher than I am used to in the analogue world, not a showstopper as my project is a sub controller BUT at this time I would not consider it for much else!! This level was later confirmed using REW to measure it after calibration.

Please note the measurements are independent of the PC audio path BUT they do depend on the USB connection so performance may improve when there is no USB connection (my project has yet to reach the stage where I can safely cast the DSP adrift into standalone).

Hope this helps anybody considering this chip, otherwise it does what it says on the tin, I had to build my own boards and programming gear as like most of its fellows the development kits are extortionately expensive for most folks!!
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Old 23rd July 2015, 10:11 AM   #2
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Join Date: Apr 2003
Location: Tampere Finland Europe
Elektor Electronics and FreeDSP designs (boards) are not expensive, but I think we need a brand new ADAU1701 board with separate ADC chip (PCM1804 or PCM1803A if unbalanced input is enough) and an extra DAC. A DAC chip like the TDA1387T would be fine for an extra channel pair for (sub)woofers.
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