diff --git a/app/src/main/assets/config b/app/src/main/assets/config
index 8699778e..4ef2163e 100644
--- a/app/src/main/assets/config
+++ b/app/src/main/assets/config
@@ -19,7 +19,7 @@ rtcp_mux no
 jitter_buffer_delay 5-10
 rtp_stats no
 dyn_dns yes
-prefer_ipv6 no
+net_prefer_ipv6 no
 module ilbc.so
 module g7221.so
 module g711.so
@@ -39,9 +39,12 @@ module_app debug_cmd.so
 module_app mwi.so
 evdev_device /dev/input/event0
 opus_bitrate 28000
+opus_samplerate 16000
 opus_cbr no
 opus_inbandfec yes
 opus_application voip
+opus_stereo no
+opus_sprop_stereo no
 ice_turn no
 ice_debug no
 ice_nomination regular
diff --git a/app/src/main/kotlin/com/tutpro/baresip/Config.kt b/app/src/main/kotlin/com/tutpro/baresip/Config.kt
index 4dcbe34b..4290a881 100644
--- a/app/src/main/kotlin/com/tutpro/baresip/Config.kt
+++ b/app/src/main/kotlin/com/tutpro/baresip/Config.kt
@@ -37,6 +37,22 @@ object Config {
             config = "${config}opus_application voip\n"
             write = true
         }
+        if (!config.contains("opus_samplerate")) {
+            config = "${config}opus_samplerate 16000\n"
+            val accountsFile = File(BaresipService.filesPath + "/config")
+            var accounts = Utils.getFileContents(accountsFile)
+            accounts = accounts.replace("opus/48000/1", "opus/16000/1")
+            Utils.putFileContents(accountsFile, accounts)
+            write = true
+        }
+        if (!config.contains("opus_stereo")) {
+            config = "${config}opus_stereo no\n"
+            write = true
+        }
+        if (!config.contains("opus_sprop_stereo")) {
+            config = "${config}opus_sprop_stereo no\n"
+            write = true
+        }
         if (!config.contains("log_level")) {
             config = "${config}log_level 2\n"
             Api.log_level_set(2)
@@ -47,9 +63,16 @@ object Config {
             Api.log_level_set(ll)
             Log.logLevelSet(ll)
         }
-        if (!config.contains("prefer_ipv6")) {
-            config = "prefer_ipv6 no\n${config}"
+        val preferIpv6 = variable("prefer_ipv6")
+        if (preferIpv6.size > 0) {
+            remove("prefer_ipv6")
+            config = "net_prefer_ipv6 ${preferIpv6[0]}\n${config}"
             write = true
+        } else {
+            if (!config.contains("net_prefer_ipv6")) {
+                config = "net_prefer_ipv6 no\n${config}"
+                write = true
+            }
         }
         if (!config.contains("call_volume")) {
             config = "${config}call_volume 0\n"
diff --git a/app/src/main/kotlin/com/tutpro/baresip/ConfigActivity.kt b/app/src/main/kotlin/com/tutpro/baresip/ConfigActivity.kt
index e9aa941a..d257ee96 100644
--- a/app/src/main/kotlin/com/tutpro/baresip/ConfigActivity.kt
+++ b/app/src/main/kotlin/com/tutpro/baresip/ConfigActivity.kt
@@ -52,7 +52,7 @@ class ConfigActivity : AppCompatActivity() {
         listenAddr.setText(oldListenAddr)
 
         preferIPv6 = findViewById(R.id.PreferIPv6) as CheckBox
-        val piCv = Config.variable("prefer_ipv6")
+        val piCv = Config.variable("net_prefer_ipv6")
         oldPreferIPv6 = if (piCv.size == 0) "no" else piCv[0]
         preferIPv6.isChecked = oldPreferIPv6 == "yes"
 
@@ -154,7 +154,7 @@ class ConfigActivity : AppCompatActivity() {
             var preferIPv6String = "no"
             if (preferIPv6.isChecked) preferIPv6String = "yes"
             if (oldPreferIPv6 != preferIPv6String) {
-                Config.replace("prefer_ipv6", preferIPv6String)
+                Config.replace("net_prefer_ipv6", preferIPv6String)
                 save = true
                 restart = true
             }