Merge pull request #206 from Allan-xmos/feature/48k_filter_design

add 48k filter design, small tweak to optimised scaling

CHANGELOG.rst

@@ -1,6 +1,11 @@
 lib_mic_array change log
 ========================
 
+5.2.0
+-----
+
+  * Added 48 kHz decimator design script
+
 5.1.0
 -----
 

lib_mic_array/module_build_info

@@ -1,4 +1,4 @@
-VERSION = 5.0.3
+VERSION = 5.2.0
 
 DEPENDENT_MODULES = lib_xcore_math 
 

script/filter_design/design_filter.py

@@ -320,6 +320,44 @@ def good_32k_filter(int_coeffs: bool):
     return coeffs
 
 
+def good_48k_filter(int_coeffs: bool):
+    fs_0 = 3072000
+    decimations = [32, 2]
+
+    # stage 1 parameters
+    ma_stages = 5
+
+    # stage 2 parameters
+    cutoff = 20000
+    transition_bandwidth = 1000
+    taps_2 = 96
+    fir_window = ("kaiser", 6.5)
+    stage_2 = stage_params(cutoff, transition_bandwidth, taps_2, fir_window)
+
+    coeffs = design_2_stage(fs_0, decimations, ma_stages, stage_2, int_coeffs=int_coeffs)
+
+    return coeffs
+
+
+def small_48k_filter(int_coeffs: bool):
+    fs_0 = 3072000
+    decimations = [32, 2]
+
+    # stage 1 parameters
+    ma_stages = 5
+
+    # stage 2 parameters
+    cutoff = 20000
+    transition_bandwidth = 1000
+    taps_2 = 64
+    fir_window = ("kaiser", 8)
+    stage_2 = stage_params(cutoff, transition_bandwidth, taps_2, fir_window)
+
+    coeffs = design_2_stage(fs_0, decimations, ma_stages, stage_2, int_coeffs=int_coeffs)
+
+    return coeffs
+
+
 def main():
     coeffs = small_2_stage_filter(int_coeffs=True)
     out_path = "small_2_stage_filter_int.pkl"
@@ -333,10 +371,20 @@ def main():
     out_path = "good_3_stage_filter_int.pkl"
     ft.save_packed_filter(out_path, coeffs)
 
+    # For more info on 32kHz and 48kHz design, see
+    # https://xmosjira.atlassian.net/wiki/spaces/CONF/pages/3805052950/32k+and+48k+Hz+lib+mic+array
+
     coeffs = good_32k_filter(int_coeffs=True)
     out_path = "good_32k_filter_int.pkl"
     ft.save_packed_filter(out_path, coeffs)
 
+    coeffs = good_48k_filter(int_coeffs=True)
+    out_path = "good_48k_filter_int.pkl"
+    ft.save_packed_filter(out_path, coeffs)
+
+    coeffs = small_48k_filter(int_coeffs=True)
+    out_path = "small_48k_filter_int.pkl"
+    ft.save_packed_filter(out_path, coeffs)
 
 if __name__ == "__main__":
     main()

script/filter_design/filter_tools.py

@@ -87,8 +87,16 @@ def moving_average_filter_int16(decimation_ratio, n_stages, optimise_scaling=Tru
             # with the next stage. Use a 2 stage MA again for the final convolution
             rounding_stages = n_stages - 3
             if n_stages > 5:
-                # rounding could add up to len(b) to the value, compensate scaling
-                max_value = (32767.0 - len(b)*rounding_stages)
+                # rounding could add up to len(b) to the value, compensate scaling,
+                # not all values have been tested, so some may fail
+                if n_stages in [5]:
+                    max_value = (32767.0 - len(b))
+                elif n_stages in [7, 8]:
+                    # hand tuned to get lucky on the rounding, there's probably a nicer way
+                    max_value = (32767.0 - 7*len(b))
+                else:
+                    # sometimes adds up to more than len(b), add extra to be safe
+                    max_value = (32767.0 - len(b)*n_stages)
             else:
                 max_value = 32767.0
             scaling = np.max(b)/max_value