diff --git a/lib/synth-audio.js b/lib/synth-audio.js
index b07994f..514cb72 100644
--- a/lib/synth-audio.js
+++ b/lib/synth-audio.js
@@ -303,27 +303,7 @@ const synthIbm = async(logger, {credentials, stats, voice, text}) => {
   }
 };
 
-async function synthMicrosoft(logger, {
-  credentials,
-  stats,
-  language,
-  voice,
-  text,
-  filePath
-}) {
-  const synthFunc = process.env.JAMBONZ_ONPREM_AZURE_SYNTHESIZE_BY_HTTP ?
-    _synthMicrosoftByHttp : _synthMicrosoftBySdk;
-  return await synthFunc(logger, {
-    credentials,
-    stats,
-    language,
-    voice,
-    text,
-    filePath
-  });
-}
-
-async function _synthMicrosoftByHttp(logger, {
+async function _synthOnPremMicrosoft(logger, {
   credentials,
   stats,
   language,
@@ -364,7 +344,7 @@ async function _synthMicrosoftByHttp(logger, {
   }
 }
 
-const _synthMicrosoftBySdk = async(logger, {
+const synthMicrosoft = async(logger, {
   credentials,
   stats,
   language,
@@ -374,18 +354,19 @@ const _synthMicrosoftBySdk = async(logger, {
 }) => {
   try {
     const {api_key: apiKey, region, use_custom_tts, custom_tts_endpoint, custom_tts_endpoint_url} = credentials;
+    if (use_custom_tts && custom_tts_endpoint_url) {
+      return await _synthOnPremMicrosoft(logger, {
+        credentials,
+        stats,
+        language,
+        voice,
+        text,
+        filePath
+      });
+    }
     const trimSilence = filePath.endsWith('.r8');
     let content = text;
-    let speechConfig;
-    if (use_custom_tts && custom_tts_endpoint_url) {
-      if (apiKey) {
-        speechConfig = SpeechConfig.FromHost(new URL(custom_tts_endpoint_url), apiKey);
-      } else {
-        speechConfig = SpeechConfig.FromHost(new URL(custom_tts_endpoint_url));
-      }
-    } else {
-      speechConfig = SpeechConfig.fromSubscription(apiKey, region);
-    }
+    const speechConfig = SpeechConfig.fromSubscription(apiKey, region);
     speechConfig.speechSynthesisLanguage = language;
     speechConfig.speechSynthesisVoiceName = voice;
     if (use_custom_tts && custom_tts_endpoint) {