IIR inconsistencies and documentation problems (DSP-123)

[Bobobel]

I do read all and that moreover several times!

Dear Dimitry!
Your doing a great and valuable job.
IIR is running, so no complaint from my side.
But some little problems with results in irr example (LP).

Environment

• Development Kit: ESP32S3-BOX-3
• Kit version Sorry, I do not see it
• Module or chip used: ESP32S3
• IDF version VSCode Espressif v1.6.5 but same with IDF 5.1.2
• Build System: [CMake]
• Compiler version C:/Espressif/tools/tools/xtensa-esp32s3-elf/esp-12.2.0_20230208/xtensa-esp32s3-elf/bin/xtensa-esp32s3-elf-gcc.exe
• Operating System: [Windows]
• Power Supply: [USB]

Problem Description

1. if I call as is given in Espressif docs: dsps_fft2r_fc32_aes3_
   with underline, I have to handle extra w resp. delay.
   Giving {0,0} as suggested and used for coef gen will result in completely irregular spectrum with max[33]=inf for N=1024 in your example.
   If I call dsps_fft2r_fc32_aes3 (not so discribed in the docs), I can avoid extra w and everything with spectrum for Q=1 (see below) ist OK.

2. I had a lot of problems with dsps_view's scalings. In a first attempt I could not find the cut-off frequency nor the drop down.

So maybe this will help other people:
please use at least dsps_view(y_cf, N/2, 128, 49, -48, 0, '-')
now each vertical step is 1dB (so far as I do understand it) and each horizontal step is sample_freq(fs)/N4.
When you understand N=1024 as fs apporx. 1000 Hz you see 4Hz in each step. Now the cutoff is at xpos="26", that means 104Hz or 0.1 in the logic of dsp.
you can also see a dropdown of -18dB upt to xpos="62", that is a span of 374=148Hz. Take 2/3 then you have -12dB for an octave as expected for "biquad".
With that knowledge I could even reproduce the position and amount of Q=10 "buggle". Nice!

3. dsps_view_spectrum: I do not see any spectrum if I input a signal as suggested in the docs. I is more or less same as dsps_view when you handle power spectrum data. It shows without asking '|' char plot.

4. I did not find any speedup for the IIR calculation with ESP32S3 optimized code (dsps_biquad_f32_aes3) againt pur _f32

Expected Behavior

Could you please expand the poor documentation for not sooo (!) experienced users?
Same holds for the use of the delay, for which I do not find any doc.
Same holds for the use of the dsps_view_spectrum: what is its benefit?

Actual Behavior

Steps to repropduce

use your example!

Thanks for the nice component.