refactor: overhaul config.py, remove cli default options

7 files changed, 120 insertions, 256 deletions

diff --git a/app/converter/clients/__init__.py b/app/converter/clients/__init__.py
index d02fd9f..16fc99c 100644
--- a/app/converter/clients/__init__.py
+++ b/app/converter/clients/__init__.py
@@ -19,7 +19,7 @@ from .base import BaseTTSClient, ConversionCancelled, VOICE_MODE_CLONE, \
 from .languages import LANGUAGE_CHOICES, LANGUAGE_ISO_CODES, TTS_LANGUAGES, \
     TTS_LANGUAGE_ALIASES, normalize_language
 from .speakers import QWEN3_TTS_SPEAKERS, SPEAKER_DISPLAY_NAMES, \
-    is_builtin_speaker, speaker_display_name, speaker_display_name_for
+    is_builtin_speaker, speaker_display_name_for
 from .transcribe import (transcribe_reference_audio,
                          transcribe_reference_audio_detailed,
                          whisper_backend_available, whisper_backend_problem)
@@ -57,7 +57,7 @@ __all__ = [
     "LANGUAGE_CHOICES", "normalize_language",
     # speakers
     "QWEN3_TTS_SPEAKERS", "SPEAKER_DISPLAY_NAMES",
-    "speaker_display_name", "speaker_display_name_for", "is_builtin_speaker",
+    "speaker_display_name_for", "is_builtin_speaker",
     # transcription
     "transcribe_reference_audio", "transcribe_reference_audio_detailed",
     "whisper_backend_available", "whisper_backend_problem",
diff --git a/app/converter/clients/audiocpp.py b/app/converter/clients/audiocpp.py
index 8c446d3..da8d364 100644
--- a/app/converter/clients/audiocpp.py
+++ b/app/converter/clients/audiocpp.py
@@ -16,8 +16,7 @@ from ..chunking import split_into_chunks
 from .base import (BaseTTSClient, ConversionCancelled,
                    NonRetryableTTSError, resolve_request_seed)
 from .languages import LANGUAGE_ISO_CODES, normalize_language
-from .speakers import (is_builtin_speaker, speaker_display_name,
-                       speaker_display_name_for)
+from .speakers import is_builtin_speaker, speaker_display_name_for
 
 logger = logging.getLogger(__name__)
 
@@ -215,23 +214,18 @@ class AudioCppTTSClient(BaseTTSClient):
     its voice is supplied; all three are resolved server-side from the
     request's "voice"/"instructions" fields:
 
-    - Speaker mode (--voice with a built-in speaker name, or no flag on a
-      CustomVoice entry): Qwen3-TTS CustomVoice only. A built-in speaker
-      name (e.g. "Vivian") is passed through, plus the INSTRUCT style
-      prompt. The selected entry must be the CustomVoice model (capability
+    - Speaker mode (--voice with a built-in speaker name): Qwen3-TTS
+      CustomVoice only. A built-in speaker name (e.g. "Vivian") is passed
+      through. The selected entry must be the CustomVoice model (capability
       == speaker); a speaker name on a non-speaker entry is treated as a
       server-side preset instead.
     - Preset mode (--voice NAME): a voice configured on the server
       (``voice_presets`` or ``voice_dir`` in its config, e.g. a cloning
       reference). The name is validated against GET /v1/audio/voices at
       startup because an unresolvable name would silently fall back to
-      plain TTS on a clone-based model instead of failing. When
-      AUDIOCPP_CLONE_MODEL_ID names a second server entry of the same
-      family (typically the Qwen Base model), preset requests are routed
-      to it. Selecting a non-speaker --voice on a CustomVoice primary with
-      a clone id configured is the documented way to switch a speaker setup
-      to cloning; without a clone id the voice is validated against the
-      server's voice library.
+      plain TTS on a clone-based model instead of failing. To clone on a
+      Qwen3-TTS setup, select the Base model entry with --model and pass
+      a preset voice.
     - Voice design (task "vdes" entries, e.g. Qwen3-TTS VoiceDesign): the
       voice is described in natural language through ``instructions``,
       which is required and sent with every request (no ``voice`` field).
@@ -240,12 +234,13 @@ class AudioCppTTSClient(BaseTTSClient):
 
     The entry's capability decides how an explicit --voice is read: on a
     speaker-capable entry a name that matches a built-in speaker selects
-    speaker mode, and every other name is a server-side preset. With no
-    --voice the entry's capability picks the mode: design entries require
-    --instructions; speaker entries use the built-in CustomVoice speaker
-    in config.SPEAKER; clone entries (the Base model, and every other
-    family) fail fast with a hint to pass --voice, instead of silently
-    synthesizing with a random default voice.
+    speaker mode, and every other name is a server-side preset. The
+    entry's capability picks the mode: design entries require
+    --instructions; speaker entries require --voice naming a built-in
+    CustomVoice speaker; clone entries (the Base model, and every other
+    family) require --voice with a server-side preset — all fail fast
+    with a hint instead of silently synthesizing with a random default
+    voice.
 
     ``instructions`` also works on non-design entries, where it acts as a
     generic style/delivery instruction (voice control): families that read
@@ -272,11 +267,11 @@ class AudioCppTTSClient(BaseTTSClient):
                  quiet: bool = False):
         super().__init__(chunks_dir, quiet=quiet)
         self.api_url = (api_url or config.AUDIOCPP_API_URL).rstrip("/")
-        # Per-run model selection: the --model CLI flag overrides config; an
-        # empty value is resolved at connect time when the server hosts exactly
-        # one entry, so multi-model servers don't require editing config.py.
-        self.model_id = (model_id if model_id is not None
-                         else config.AUDIOCPP_MODEL_ID) or ""
+        # Per-run model selection: the --model CLI flag (or the Generate
+        # form's Model pick). An empty value is resolved at connect time
+        # when the server hosts exactly one entry, so single-model servers
+        # don't require --model.
+        self.model_id = (model_id or "").strip()
         self._model_id_explicit = bool(self.model_id)
         # Validate before connecting so bad values fail fast without a server.
         self.language = normalize_language(
@@ -290,26 +285,23 @@ class AudioCppTTSClient(BaseTTSClient):
         # resolved in _connect: a --voice that names a built-in CustomVoice
         # speaker on a speaker-capable entry selects speaker mode; every
         # other name (and any name on a clone-capable entry) is a server-side
-        # preset. preset_mode gates _select_model's reroute to
-        # AUDIOCPP_CLONE_MODEL_ID and the INSTRUCT style-prompt logic. The
-        # request's "voice" field (self.voice) is filled in _connect per the
-        # mode.
+        # preset. The request's "voice" field (self.voice) is filled in
+        # _connect per the mode.
         self.preset_mode = False
         self.speaker_mode = False
         self.voice = voice or None
         # Style/voice-design instruction sent with every request (the CLI
-        # --instructions flag overrides AUDIOCPP_INSTRUCTIONS in config.py).
+        # --instructions flag / the Generate form's Instructions field).
         # For task "vdes" entries it describes the voice to design; for other
         # families it is a generic style instruction when the model reads one.
-        self.instructions = (instructions if instructions is not None
-                             else config.AUDIOCPP_INSTRUCTIONS or "").strip()
+        self.instructions = (instructions or "").strip()
         # Free-form per-request options (--option KEY=VALUE) forwarded in the
         # request's "options" object; models ignore keys they don't know.
         self.request_options: Dict[str, str] = dict(request_options or {})
         # Set during _connect: design_mode for "vdes" entries, instruction_voice
         # when a family without built-in speakers gets its voice from the
         # instruction alone (no voice field). self.voice is also finalized
-        # there (the speaker/preset name, or config.SPEAKER for the default).
+        # there (the speaker/preset name).
         self.design_mode = False
         self.instruction_voice = False
         # Family and task of the selected model entry and the family's request
@@ -337,10 +329,9 @@ class AudioCppTTSClient(BaseTTSClient):
         mode. An explicit --voice on a speaker-capable (CustomVoice) entry
         that names a built-in speaker selects speaker mode; every other
         --voice is a server-side preset, validated against the server's
-        voice library (and rerouted to AUDIOCPP_CLONE_MODEL_ID when set).
-        With no --voice, design entries require --instructions, speaker-
-        capable entries use the built-in config.SPEAKER, and clone entries
-        fail fast with a hint instead of silently synthesizing with a
+        voice library. Without a --voice, design entries require
+        --instructions and every other capability requires --voice — the
+        run fails fast with a hint instead of silently synthesizing with a
         random default voice.
         """
         self._check_health()
@@ -351,8 +342,7 @@ class AudioCppTTSClient(BaseTTSClient):
             # preset. A name matching a built-in CustomVoice speaker on a
             # speaker-capable primary selects speaker mode; every other name
             # (and any name when the primary entry is absent) is a preset,
-            # validated against the server's voice library and rerouted to
-            # AUDIOCPP_CLONE_MODEL_ID when configured.
+            # validated against the server's voice library.
             primary = next((m for m in models if m["id"] == self.model_id),
                            None)
             if primary is not None:
@@ -367,10 +357,8 @@ class AudioCppTTSClient(BaseTTSClient):
                     self.speaker_mode = True
                     self._connected(f"speaker '{self.voice}'")
             if not self.speaker_mode:
-                # Server-side preset (--voice): validate it and route to
-                # the clone model entry when AUDIOCPP_CLONE_MODEL_ID is set.
+                # Server-side preset (--voice): validate it.
                 self.preset_mode = True
-                self._select_model(models)
                 self._require_model_id(models)
                 self._resolve_family(models)
                 self._resolve_task(models)
@@ -401,10 +389,13 @@ class AudioCppTTSClient(BaseTTSClient):
                 self._connected("voice design")
                 self._report(f"[INFO] Designing the voice from: {self.instructions}")
             elif capability == AUDIOCPP_VOICE_SPEAKER:
-                # No flag on a CustomVoice entry: the built-in config.SPEAKER.
-                self.voice = speaker_display_name()
-                self.speaker_mode = True
-                self._connected(f"speaker '{self.voice}'")
+                # No --voice on a CustomVoice entry: refuse instead of
+                # guessing a built-in speaker.
+                raise RuntimeError(
+                    f"The audio.cpp model '{self.model_id}' (family "
+                    f"'{self.family}') serves built-in speakers: pass "
+                    "--voice NAME with one of them (e.g. Vivian, Ryan, "
+                    "Uncle Fu) to synthesize with it (see README).")
             elif self.instructions:
                 # Families without built-in speakers can still get their voice
                 # from the instruction alone (e.g. OmniVoice voice design).
@@ -523,11 +514,8 @@ class AudioCppTTSClient(BaseTTSClient):
     def _auto_pick_model_id(self, models: List[Dict[str, str]]) -> None:
         """Resolve an empty model id when the server hosts exactly one entry.
 
-        Multi-model servers generated with several lazily-loaded entries can
-        be used without editing app/converter/config.py: leave AUDIOCPP_MODEL_ID
-        (and ``--model``) unset, and the single hosted entry is chosen
-        automatically. With more than one entry an explicit choice is required
-        (via ``--model`` or AUDIOCPP_MODEL_ID), since guessing would risk
+        Multi-model servers generated with several lazily-loaded entries
+        need an explicit ``--model``, since guessing would risk
         synthesizing a whole book with the wrong family.
         """
         if self.model_id:
@@ -535,22 +523,16 @@ class AudioCppTTSClient(BaseTTSClient):
         if len(models) == 1:
             self.model_id = models[0]["id"]
             logger.info(
-                "AUDIOCPP_MODEL_ID is unset; using the only server entry '%s'",
+                "No --model given; using the only server entry '%s'",
                 self.model_id)
         else:
             logger.debug(
-                "AUDIOCPP_MODEL_ID is unset and the server hosts %d entries; "
-                "an explicit --model or config id is required",
+                "No --model given and the server hosts %d entries; "
+                "an explicit --model is required",
                 len(models))
 
     def _require_model_id(self, models: List[Dict[str, str]]) -> None:
-        """Verify the model id chosen for this run exists on the server.
-
-        Speaker mode needs AUDIOCPP_MODEL_ID (the CustomVoice entry).
-        Preset mode validates whichever id _select_model resolved, so a
-        server hosting only a cloning model works for --voice. The default
-        error distinguishes the two so the fix is obvious.
-        """
+        """Verify the model id chosen for this run exists on the server."""
         model_ids = [model["id"] for model in models]
         if self.model_id and self.model_id in model_ids:
             return
@@ -559,19 +541,14 @@ class AudioCppTTSClient(BaseTTSClient):
             raise RuntimeError(
                 f"The audio.cpp server at {self.api_url} hosts {len(model_ids)} "
                 f"model entries ({configured}); audiobook.py needs to know which "
-                "one to use. Pass --model <id> when converting, or set "
-                "AUDIOCPP_MODEL_ID in app/converter/config.py to one of them "
-                "(see README)."
+                "one to use. Pass --model <id> when converting (see README)."
             )
         if self.preset_mode:
             raise RuntimeError(
                 f"The audio.cpp server at {self.api_url} has no model id "
-                f"'{self.model_id}' or clone model id "
-                f"'{config.AUDIOCPP_CLONE_MODEL_ID}' (configured: {configured}). "
-                "Add a TTS model entry for the family you want to the server "
-                "config and match AUDIOCPP_MODEL_ID / AUDIOCPP_CLONE_MODEL_ID "
-                "in app/converter/config.py to its id, or select it per run with "
-                "--model (see README)."
+                f"'{self.model_id}' (configured: {configured}). Pass "
+                "--model <id> naming one of the hosted TTS model entries "
+                "(see README)."
             )
         raise RuntimeError(
             f"The audio.cpp server at {self.api_url} has no model id "
@@ -581,52 +558,6 @@ class AudioCppTTSClient(BaseTTSClient):
             "on any TTS model (see README)."
         )
 
-    def _select_model(self, models: List[Dict[str, str]]) -> None:
-        """Pick the model for preset (cloning) requests.
-
-        Defaults to the primary model id. When AUDIOCPP_CLONE_MODEL_ID is
-        configured and present on the server, preset requests are routed
-        to it instead, so one server can host the CustomVoice model for
-        speaker mode and the Base model for cloning (Qwen3-TTS setups).
-        A clone id that names a model of a different family is ignored
-        with a warning, since preset requests must synthesize with the
-        family the run is configured for.
-        """
-        clone_model_id = config.AUDIOCPP_CLONE_MODEL_ID
-        if not clone_model_id or clone_model_id == self.model_id:
-            return
-        families = {model["id"]: model["family"] for model in models}
-        if clone_model_id not in families:
-            # A qwen3_tts primary without its clone entry silently degrades
-            # (presets are ignored on the CustomVoice model), so that case
-            # keeps the warning; single-model servers of other families are
-            # the normal configuration and only get a debug note.
-            primary_family = families.get(self.model_id) or ""
-            if primary_family == AUDIOCPP_FAMILY_QWEN3_TTS:
-                logger.warning(
-                    "AUDIOCPP_CLONE_MODEL_ID %r is not configured on the audio.cpp "
-                    "server; preset requests use '%s' instead",
-                    clone_model_id, self.model_id)
-            else:
-                logger.debug(
-                    "AUDIOCPP_CLONE_MODEL_ID %r is not configured on the audio.cpp "
-                    "server; preset requests use '%s' instead",
-                    clone_model_id, self.model_id)
-            return
-        primary_family = families.get(self.model_id)
-        clone_family = families[clone_model_id]
-        if primary_family and clone_family and primary_family != clone_family:
-            logger.warning(
-                "AUDIOCPP_CLONE_MODEL_ID %r hosts family %r, but "
-                "AUDIOCPP_MODEL_ID %r hosts %r; preset requests stay on "
-                "'%s'. Point both ids at the same model entry in "
-                "app/converter/config.py (single-model servers use the same id "
-                "for both)",
-                clone_model_id, clone_family, self.model_id, primary_family,
-                self.model_id)
-            return
-        self.model_id = clone_model_id
-
     def _resolve_family(self, models: List[Dict[str, str]]) -> None:
         """Resolve the selected model's family and its request profile.
 
@@ -730,11 +661,6 @@ class AudioCppTTSClient(BaseTTSClient):
             # Explicit voice-design or style instruction (required for task
             # "vdes" entries; a Ctrl/style control on families that read it).
             payload["instructions"] = self.instructions
-        elif not self.preset_mode and config.INSTRUCT \
-                and self.profile.sends_instructions:
-            # Style instruction for the Qwen3-TTS CustomVoice speakers;
-            # ignored by the Base (cloning) model and other families.
-            payload["instructions"] = config.INSTRUCT
         if self.request_options:
             # Generic per-model controls (--option KEY=VALUE): forwarded
             # verbatim; the model ignores keys it does not know.
diff --git a/app/converter/clients/faster.py b/app/converter/clients/faster.py
index f0874e0..48c26ab 100644
--- a/app/converter/clients/faster.py
+++ b/app/converter/clients/faster.py
@@ -33,7 +33,13 @@ class FasterTTSClient(BaseTTSClient):
                  voice: Optional[str] = None, api_url: Optional[str] = None,
                  quiet: bool = False):
         super().__init__(chunks_dir, quiet=quiet)
-        self.voice = voice or config.FASTER_VOICE
+        # The voice is per-run (--voice / the Generate form's Voice pick);
+        # there is no configured default.
+        self.voice = (voice or "").strip()
+        if not self.voice:
+            raise RuntimeError(
+                "The faster backend requires a voice: pass --voice NAME "
+                "naming a key in the server's voices.json (see README).")
         self.api_url = (api_url or config.FASTER_API_URL).rstrip("/")
         self._check_health()
 
diff --git a/app/converter/clients/qwen.py b/app/converter/clients/qwen.py
index ed3149b..17f14c5 100644
--- a/app/converter/clients/qwen.py
+++ b/app/converter/clients/qwen.py
@@ -15,7 +15,7 @@ from .base import (BaseTTSClient, ConversionCancelled, resolve_request_seed,
                    VOICE_MODE_CLONE, VOICE_MODE_CUSTOM, VOICE_MODE_DESIGN,
                    VOICE_MODES)
 from .languages import normalize_language
-from .speakers import speaker_display_name
+from .speakers import QWEN3_TTS_SPEAKERS, speaker_display_name_for
 
 logger = logging.getLogger(__name__)
 
@@ -32,7 +32,8 @@ class QwenTTSClient(BaseTTSClient):
                  voice_mode: str = "custom_voice", voice_clone_ref_audio: Optional[str] = None,
                  voice_clone_ref_text: Optional[str] = None, skip_transcription: bool = False,
                  language: Optional[str] = None, api_url: Optional[str] = None,
-                 instructions: Optional[str] = None, quiet: bool = False):
+                 instructions: Optional[str] = None, quiet: bool = False,
+                 voice: Optional[str] = None):
         super().__init__(chunks_dir, quiet=quiet)
         if voice_mode not in VOICE_MODES:
             raise ValueError(
@@ -42,11 +43,17 @@ class QwenTTSClient(BaseTTSClient):
         self.voice_clone_ref_audio = voice_clone_ref_audio
         self.voice_clone_ref_text = (voice_clone_ref_text or "").strip()
         self.skip_transcription = skip_transcription
+        # Built-in CustomVoice speaker (VOICE_MODE_CUSTOM): the --voice
+        # value / the Generate form's Speaker pick. Required there — there
+        # is no configured default speaker.
+        self.speaker = (voice or "").strip() or None
+        if voice_mode == VOICE_MODE_CUSTOM and not self.speaker:
+            raise ValueError(
+                "CustomVoice mode requires a speaker: pass --voice SPEAKER "
+                f"(one of {', '.join(QWEN3_TTS_SPEAKERS)})")
         # Voice design / style instruction (VoiceDesign mode): describes the
-        # voice to design. Defaults to the configured CustomVoice INSTRUCT so
-        # a run never sends an empty design prompt.
-        self.instructions = (instructions if instructions is not None
-                             else config.INSTRUCT).strip()
+        # voice to design. Required there (validated by the converter).
+        self.instructions = (instructions or "").strip()
         # api_url overrides the configured endpoint for the active voice mode
         # (used by the hub's "[remote]" backend entries and --api-url).
         self.api_url = (api_url or "").strip() or None
@@ -261,21 +268,19 @@ class QwenTTSClient(BaseTTSClient):
     # ------------------------------------------------------------------
 
     def _generate_custom_voice(self, text: str) -> Tuple:
-        """Generate audio using CustomVoice mode."""
+        """Generate audio using CustomVoice mode with the run's speaker."""
         custom_api = self._resolve_api_name("/run_instruct", "/run_custom_voice", "/generate_custom_voice")
         if custom_api == "/run_instruct":
             payload = dict(
                 text=text,
                 lang_disp=self.language,
-                spk_disp=speaker_display_name(),
-                instruct=config.INSTRUCT,
+                spk_disp=speaker_display_name_for(self.speaker),
             )
         else:
             payload = dict(
                 text=text,
                 language=self.language,
-                speaker=config.SPEAKER,
-                instruct=config.INSTRUCT,
+                speaker=self.speaker,
             )
             if self._endpoint_accepts_param(custom_api, "model_id_cv"):
                 payload["model_id_cv"] = CUSTOM_VOICE_MODEL_ID
@@ -323,7 +328,7 @@ class QwenTTSClient(BaseTTSClient):
 
         clone_api = self._resolve_api_name("/run_voice_clone", "/generate_voice_clone",
                                            api_info=self.clone_api_info)
-        use_xvector = config.XVECTOR_ONLY or not self.voice_clone_ref_text
+        use_xvector = not self.voice_clone_ref_text
 
         if clone_api == "/run_voice_clone":
             payload = dict(
diff --git a/app/converter/clients/speakers.py b/app/converter/clients/speakers.py
index eecd52a..a68af68 100644
--- a/app/converter/clients/speakers.py
+++ b/app/converter/clients/speakers.py
@@ -2,13 +2,11 @@
 
 from typing import Optional
 
-from .. import config
-
 # Built-in CustomVoice speaker names for the Qwen3-TTS family. Shared by the
-# qwen-tts demo backend (config.SPEAKER, the qwen setup/form) and the
-# audio.cpp audiocpp backend's CustomVoice entry (the Convert form's Speaker
-# picker). Entries are the canonical/config form; speaker_display_name()
-# maps them to the wire (display) form via SPEAKER_DISPLAY_NAMES below.
+# qwen-tts demo backend (the qwen setup/form) and the audio.cpp audiocpp
+# backend's CustomVoice entry (the Convert form's Speaker picker). Entries
+# are the canonical form; speaker_display_name_for() maps them to the wire
+# (display) form via SPEAKER_DISPLAY_NAMES below.
 QWEN3_TTS_SPEAKERS = ("Vivian", "Serena", "Uncle_Fu", "Dylan", "Eric",
                       "Ryan", "Aiden", "Ono_Anna", "Sohee")
 
@@ -50,8 +48,3 @@ def is_builtin_speaker(name: Optional[str]) -> bool:
     norm = name.lower().replace("_", " ").replace("-", " ")
     return any(norm == speaker.lower().replace("_", " ")
                for speaker in QWEN3_TTS_SPEAKERS)
-
-
-def speaker_display_name() -> str:
-    """Return the display name for the configured custom speaker."""
-    return speaker_display_name_for(config.SPEAKER)
diff --git a/app/converter/config.py b/app/converter/config.py
index e37269b..3511033 100644
--- a/app/converter/config.py
+++ b/app/converter/config.py
@@ -3,119 +3,43 @@ AUDIO_FORMAT = "m4b"
 AUDIO_BITRATE = "128k"
 LANGUAGE = "English"
 
-API_TIMEOUT = 600  # Timeout per chunk request in seconds
-MAX_RETRIES = 3    # Attempts per chunk request
+API_TIMEOUT = 600                # Timeout per chunk request in seconds
+MAX_RETRIES = 3                  # Attempts per chunk request
 HEARTBEAT_INTERVAL_SECONDS = 30  # Print "still working" in console logs every N seconds
 
 # Words per TTS generation request (client-side chunking).
 CHUNK_SIZE = 250
 
 # Where books are read from and where finished audiobooks are written.
-# Relative paths resolve against the project root (the folder containing
-# audiobook.py). The --input/--output CLI flags override these per run.
+# Relative paths resolve against the project root.
 INPUT_DIR = "./input"
 OUTPUT_DIR = "./output"
 
-# Playback speed factor for the final audiobook (1.0 = normal).
-# Pitch-preserving. The --speed CLI flag overrides this per run.
+# Output audiobook file at a different tempo.
 SPEED = 1.0
 
-# Dump each chunk's raw audio and the exact text sent for it under the
-# debug/ folder (organized per book and chapter), and log every TTS
-# request and response to the console and log file. The --debug CLI flag
-# forces this on for a single run.
+# Dump each chunk's raw audio and the text sent for it into debug/
 DEBUG = False
 
-# Default for "Stop server and exit" (TUI Settings menu: "Stop server
-# and exit"): automatically stop the TTS server and exit the TUI after
-# generating audiobooks.
+# Default option for stop and exit TTS server after generating with TUI
 STOP_SERVER_AND_EXIT = True
 
-# Default TTS backend.
-# audiocpp: audiocpp_server
-# qwen: qwen-tts-demo
-# faster: faster-qwen-tts
-# The --backend CLI flag overrides this
-BACKEND = "audiocpp"
+# The IP/port that locally-managed TTS server instances run on
+QWEN_API_URL     = "http://127.0.0.1:7860"
+FASTER_API_URL   = "http://127.0.0.1:8000"
+AUDIOCPP_API_URL = "http://127.0.0.1:8080"
 
-###############################################################################
-# BACKEND 1: qwen-tts-demo (qwen) options                                       #
-###############################################################################
-
-# The qwen backend runs ONE demo server at a time, on this port. Which model
-# the server hosts is chosen per run on the Generate Audiobooks screen and
-# persisted below (see QWEN_MODEL); switching models restarts the server.
-QWEN_API_URL     = "http://127.0.0.1:7860"  # single qwen-tts-demo server
-
-# Remote (externally-run) server URL. The hub probes it and offers a
-# "[remote]" backend entry when it answers with a known qwen-tts demo (any
-# of the three models), so an externally-started server can be used alongside
-# a locally-managed one. Leave empty to disable remote probing. The default
-# matches the local port so an external server squatting the local port is
-# found without any configuration.
+# The URI used to discover externally-run instances
 QWEN_REMOTE_URL  = "http://127.0.0.1:7860"
-
-# Which model the managed demo server runs (one server hosts one model):
-#   CustomVoice - built-in speakers (see SPEAKER)
-#   Base        - voice cloning from a reference .wav
-#   VoiceDesign - voice described by an instruction
-# Chosen per run in the Generate-audiobooks form; edited here only as the
-# default for the next run.
-QWEN_MODEL = "CustomVoice"
-
-# Custom voice options
-SPEAKER = "Vivian"  #Vivian, Serena, Uncle_Fu, Dylan, Eric, Ryan, Aiden, Ono_Anna, Sohee
-# Style/delivery instruction for CustomVoice runs; also the default design
-# instruction when a VoiceDesign run does not override it.
-INSTRUCT = "Speak naturally and clearly, as if reading a dramatic book to an adult audience."
-
-# Don't clone with transcription, only use x-vector-only cloning. Generally "worse"
-XVECTOR_ONLY = False
+FASTER_REMOTE_URL = "http://127.0.0.1:8000"
+AUDIOCPP_REMOTE_URL = "http://127.0.0.1:8080"
 
 # Randomization seed. -1 means randomize with every generation
 # With SEED = -1 and CONSTANT_SEED = True, one random seed will be used for the entire audiobook.
-# This may keep the voice slightly more consistent across chunk boundaries
+# This MAY keep the voice slightly more consistent across chunk boundaries
 SEED = -1
 CONSTANT_SEED = False
 
-###############################################################################
-# BACKEND 2: faster-qwen-tts options                                          #
-###############################################################################
-FASTER_API_URL   = "http://127.0.0.1:8000"    # faster-qwen3-tts server (Base model only)
-FASTER_REMOTE_URL = "http://127.0.0.1:8000"   # externally-run faster-qwen3-tts server ("" disables probing)
-
-# Default voice if no --voice is passed
-FASTER_VOICE = "narrator"
-
-###############################################################################
-# BACKEND 3: audio.cpp options                                                #
-###############################################################################
-AUDIOCPP_API_URL = "http://127.0.0.1:8082"  # audio.cpp audiocpp_server
-AUDIOCPP_REMOTE_URL = "http://127.0.0.1:8080"  # externally-run audiocpp_server ("" disables probing)
-
-# Model ids in the audio.cpp server.json config. AUDIOCPP_MODEL_ID may point
-# at any TTS model entry the server hosts; the family is detected from the
-# server at startup and adapts the request automatically. Only qwen3_tts has
-# built-in speakers (speaker mode); every other family needs --voice with a
-# server-side voice preset. The server entry id is the model package's
-# target_directory name (e.g. "Qwen3-TTS-12Hz-1.7B-Base-GGUF"). For
-# single-model servers, set AUDIOCPP_CLONE_MODEL_ID to the same id as
-# AUDIOCPP_MODEL_ID (or leave it empty); for Qwen3-TTS it typically names a
-# second entry with the Base (cloning) model. Both default to empty so a
-# single-entry server is auto-selected; a multi-model server (one server.json
-# hosting several lazily-loaded entries) needs no editing here either: leave
-# AUDIOCPP_MODEL_ID unset to auto-select when only one entry is hosted, or
-# pick the entry per run with the --model CLI flag.
-AUDIOCPP_MODEL_ID = "Qwen3-TTS-12Hz-1.7B-Base-GGUF"
-AUDIOCPP_CLONE_MODEL_ID = "Qwen3-TTS-12Hz-1.7B-Base-GGUF"
-
-# Voice design / style instruction sent with every audio.cpp request when
-# the --instructions CLI flag is not given. Required for server entries
-# hosted with task "vdes" (voice design models such as Qwen3-TTS
-# VoiceDesign); on other families it acts as a style/delivery instruction
-# when the model supports one and is ignored otherwise. Empty by default.
-AUDIOCPP_INSTRUCTIONS = ""
-
 # Ask the audio.cpp server to unload all currently loaded models before
 # converting, so models left resident by earlier runs free their memory
 # (e.g. VRAM on GPU backends) and only the selected entry loads. Set to
diff --git a/app/converter/converter.py b/app/converter/converter.py
index 5235991..a9ea7eb 100644
--- a/app/converter/converter.py
+++ b/app/converter/converter.py
@@ -31,7 +31,7 @@ from .clients import (
     FasterTTSClient,
     QwenTTSClient,
     normalize_language,
-    speaker_display_name,
+    speaker_display_name_for,
 )
 
 logger = logging.getLogger(__name__)
@@ -207,7 +207,7 @@ class AudiobookConverter:
     def __init__(self, voice_mode: str = VOICE_MODE_CUSTOM, voice_clone_ref_audio: Optional[str] = None,
                  voice_clone_ref_text: Optional[str] = None, skip_transcription: bool = False,
                  speed: float = 1.0, single_file: bool = False, output_format: str = config.AUDIO_FORMAT,
-                 language: Optional[str] = None, backend: str = config.BACKEND,
+                 language: Optional[str] = None, backend: str = None,
                  voice: Optional[str] = None, debug: bool = False,
                  model_id: Optional[str] = None,
                  instructions: Optional[str] = None,
@@ -219,6 +219,8 @@ class AudiobookConverter:
             raise ValueError(f"Speed must be a positive number, got {speed}")
         if output_format not in AUDIO_FORMATS:
             raise ValueError(f"Unsupported output format: {output_format}")
+        if backend is None:
+            raise ValueError("backend is required (pass --backend)")
         if backend not in BACKENDS:
             raise ValueError(
                 f"Unknown backend: {backend!r} (expected one of {BACKENDS})"
@@ -257,10 +259,10 @@ class AudiobookConverter:
         elif backend == BACKEND_AUDIOCPP:
             # --voice picks the voice: a built-in speaker name on the
             # CustomVoice entry, or a server-side preset (cloning)
-            # elsewhere. model_id overrides AUDIOCPP_MODEL_ID for
-            # multi-model servers; instructions describe or style the
-            # voice, request_options pass per-model controls through to
-            # the server.
+            # elsewhere. model_id picks the server entry per run
+            # (auto-selected on single-entry servers); instructions
+            # describe or style the voice, request_options pass
+            # per-model controls through to the server.
             self.tts = AudioCppTTSClient(chunks_dir=CHUNKS_FOLDER,
                                          voice=voice, language=self.language,
                                          model_id=model_id,
@@ -270,6 +272,7 @@ class AudiobookConverter:
         else:
             # Qwen: the voice mode picks the request shape (built-in
             # speaker, clone from a reference .wav, or a designed voice);
+            # --voice names the built-in speaker in speaker mode and
             # instructions describe the voice in design mode.
             self.tts = QwenTTSClient(
                 chunks_dir=CHUNKS_FOLDER,
@@ -281,6 +284,7 @@ class AudiobookConverter:
                 instructions=self.instructions,
                 api_url=api_url,
                 quiet=quiet,
+                voice=voice,
             )
         self._progress = progress
         self.tts.cancel = cancel
@@ -314,6 +318,13 @@ class AudiobookConverter:
                 "Voice Design mode requires a voice description. "
                 "Use --instructions \"...\" to describe the voice to synthesize with."
             )
+        if self.backend == BACKEND_QWEN and self.voice_mode == VOICE_MODE_CUSTOM \
+                and not (self.voice or "").strip():
+            raise ValueError(
+                "CustomVoice mode requires a speaker. Use --voice SPEAKER "
+                "(e.g. Vivian) to pick one, or --clone / --instructions "
+                "for the other voice modes."
+            )
         if self.voice_mode == VOICE_MODE_CLONE and self.backend == BACKEND_QWEN:
             if not self.voice_clone_ref_audio:
                 raise ValueError(
@@ -348,19 +359,18 @@ class AudiobookConverter:
 
         Custom voice mode uses the built-in speaker's display name; voice
         clone mode uses the reference audio file's stem; the faster and
-        audiocpp backends use the server-side voice name (or, for audiocpp's
-        speaker mode, the selected built-in CustomVoice speaker, falling back
-        to the configured one). An instruction without a voice (voice design,
-        or instruction-defined voices on families without built-in speakers)
-        uses "designed". Spaces become underscores (e.g. "Uncle Fu" ->
-        "Uncle_Fu").
+        audiocpp backends use the server-side voice name (for audiocpp's
+        speaker mode, the selected built-in CustomVoice speaker). An
+        instruction without a voice (voice design, or instruction-defined
+        voices on families without built-in speakers) uses "designed".
+        Spaces become underscores (e.g. "Uncle Fu" -> "Uncle_Fu").
 
         Pure (no I/O, no server) so the pre-flight overwrite check can
         compute the exact output names a run would produce before spending
         time connecting to a TTS server.
         """
         if backend == BACKEND_FASTER:
-            narrator = voice or config.FASTER_VOICE
+            narrator = voice or "default"
         elif backend == BACKEND_AUDIOCPP:
             if voice:
                 narrator = voice
@@ -368,7 +378,10 @@ class AudiobookConverter:
                 # The voice comes from the instruction, not a speaker name.
                 narrator = "designed"
             else:
-                narrator = speaker_display_name()
+                # Unreachable in a valid run (the audiocpp client refuses a
+                # speaker-capable entry without --voice); keep a stable tag
+                # for the pre-flight of runs that will fail at connect time.
+                narrator = "narrator"
         elif voice_mode == VOICE_MODE_DESIGN:
             # Qwen's VoiceDesign model: the voice is described by an
             # instruction and has no speaker name.
@@ -376,7 +389,7 @@ class AudiobookConverter:
         elif voice_mode == VOICE_MODE_CLONE:
             narrator = Path(voice_clone_ref_audio).stem
         else:
-            narrator = speaker_display_name()
+            narrator = speaker_display_name_for(voice or "")
         return AudiobookConverter._sanitize_filename(
             narrator, fallback="narrator").replace(" ", "_")
 
@@ -736,7 +749,7 @@ class AudiobookConverter:
         if self.backend == BACKEND_FASTER:
             self._say(f"Faster TTS endpoint: {config.FASTER_API_URL}")
             self._say("Backend: faster (voice cloning, reference configured on server)")
-            self._say(f"Voice: {self.voice or config.FASTER_VOICE}")
+            self._say(f"Voice: {self.voice}")
         elif self.backend == BACKEND_AUDIOCPP:
             self._say(f"audio.cpp endpoint: {config.AUDIOCPP_API_URL}")
             self._say(f"Model id: {self.tts.model_id}")
@@ -750,9 +763,6 @@ class AudiobookConverter:
             elif self.instructions:
                 self._say("Backend: audio.cpp (voice from --instructions description)")
                 self._say(f"Instruction: {self.instructions}")
-            else:
-                self._say("Backend: audio.cpp (custom voice, built-in speaker)")
-                self._say(f"Speaker: {config.SPEAKER}")
             if self.request_options:
                 self._say(f"Request options: {self.request_options}")
             self._say(f"Language: {self.language}")
@@ -764,7 +774,7 @@ class AudiobookConverter:
             self._say(f"Voice mode: {self.voice_mode}")
             self._say(f"Model size: {MODEL_SIZE} (always)")
             if self.voice_mode == VOICE_MODE_CUSTOM:
-                self._say(f"Speaker: {config.SPEAKER}")
+                self._say(f"Speaker: {self.voice}")
                 self._say(f"Language: {self.language}")
             elif self.voice_mode == VOICE_MODE_CLONE:
                 self._say(f"Reference audio: {Path(self.voice_clone_ref_audio).name}")