From 0e436ded14bb8dff54716caef86928ba48a9d7be Mon Sep 17 00:00:00 2001
From: Jared Boone <jboone@earfeast.com>
Date: Fri, 29 Jan 2016 15:32:32 -0800
Subject: [PATCH] Add IIR configs for lower audio sampling rates.

---
 firmware/baseband/dsp_iir_config.hpp | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/firmware/baseband/dsp_iir_config.hpp b/firmware/baseband/dsp_iir_config.hpp
index 588e6ce80..320edb0b2 100644
--- a/firmware/baseband/dsp_iir_config.hpp
+++ b/firmware/baseband/dsp_iir_config.hpp
@@ -36,6 +36,18 @@ constexpr iir_biquad_config_t audio_48k_hpf_300hz_config {
 	{  1.00000000f, -1.94447766f,  0.94597794f }
 };
 
+// scipy.signal.butter(2, 300 / 8000.0, 'highpass', analog=False)
+constexpr iir_biquad_config_t audio_16k_hpf_300hz_config {
+	{  0.92006616f, -1.84013232f,  0.92006616f },
+	{  1.00000000f, -1.83373266f,  0.84653197f }
+};
+
+// scipy.signal.butter(2, 300 / 4000.0, 'highpass', analog=False)
+constexpr iir_biquad_config_t audio_8k_hpf_300hz_config {
+	{  0.84645925f, -1.69291851f,  0.84645925f },
+	{  1.00000000f, -1.66920314f,  0.71663387f }
+};
+
 // scipy.signal.iirdesign(wp=8000 / 24000.0, ws= 4000 / 24000.0, gpass=1, gstop=18, ftype='ellip')
 constexpr iir_biquad_config_t non_audio_hpf_config {
 	{  0.51891061f, -0.95714180f,  0.51891061f },
@@ -49,6 +61,20 @@ constexpr iir_biquad_config_t audio_48k_deemph_300_6_config {
 	{  1.00000000f, -0.96148145f,  0.00000000f }
 };
 
+// scipy.signal.butter(1, 300 / 8000.0, 'lowpass', analog=False)
+// NOTE: Technically, order-1 filter, b[2] = a[2] = 0.
+constexpr iir_biquad_config_t audio_16k_deemph_300_6_config {
+	{  0.05568894f,  0.05568894f,  0.00000000f },
+	{  1.00000000f, -0.88862213f,  0.00000000f }
+};
+
+// scipy.signal.butter(1, 300 / 4000.0, 'lowpass', analog=False)
+// NOTE: Technically, order-1 filter, b[2] = a[2] = 0.
+constexpr iir_biquad_config_t audio_8k_deemph_300_6_config {
+	{  0.10583178f,  0.10583178f,  0.00000000f },
+	{  1.00000000f, -0.78833643f,  0.00000000f }
+};
+
 // 75us RC time constant, used in broadcast FM in Americas, South Korea
 // scipy.signal.butter(1, 2122 / 24000.0, 'lowpass', analog=False)
 // NOTE: Technically, order-1 filter, b[2] = a[2] = 0.