diff --git a/docs/NOTES.md b/docs/NOTES.md
index 173bb61..da659c2 100644
--- a/docs/NOTES.md
+++ b/docs/NOTES.md
@@ -42,6 +42,8 @@ From `msttsl/mstts.inf` (`[TTSReg]`):
   - `{000031CB-3699-551F-AED0-6B4893382D57}`: "Kerry Watson", Pitch 65,
     Speaking Rate 32, Head Size 45, Expression 100, Lowering 40,
     Prominences 17, Age 30, Volume 100.
+    Measured effects per value and the change procedure are in
+    `docs/TTS-DESIGN.md` ("Flextalk profile parameters").
 - Voice data: `EngineData\AE1M08LC.*`, `AE1M11LC.*` (male, 8/11 kHz) and
   `AE2F08LC.*`, `AE2F11LC.*` (female); `.INV` inventory, `.NDX` index,
   `.COD` codebook, plus shared `DICT_CI.*`, `phondef`, `AMPRULES`, `ENDINGS`.
diff --git a/docs/TTS-DESIGN.md b/docs/TTS-DESIGN.md
index 45f6ed9..e4f403f 100644
--- a/docs/TTS-DESIGN.md
+++ b/docs/TTS-DESIGN.md
@@ -53,10 +53,12 @@ these placeholders, splits the string on whitespace, and runs the result directl
 | `{voice}` | The selected voice ID, or an empty string. |
 | `{speed}` | The rate multiplier, or an empty string when unset. |
 | `{pitch}` | The pitch offset in semitones, or an empty string when unset. |
+| `{expression}` | The Flextalk Expression profile value, or an empty string when unset. |
 
-The process also receives `VESKSLOP_TTS_VOICE`, and `VESKSLOP_TTS_SPEED` / `VESKSLOP_TTS_PITCH`
-when those are set. Write the audio to `{out}` and exit 0. Non-zero exits are errors; stderr is
-captured into the log message, so keep it short.
+The process also receives `VESKSLOP_TTS_VOICE`, `VESKSLOP_TTS_SPEED`,
+`VESKSLOP_TTS_PITCH`, and `VESKSLOP_TTS_EXPRESSION` when those are set. Write the audio to
+`{out}` and exit 0. Non-zero exits are errors; stderr is captured into the log message, so keep it
+short.
 
 Command mode is best for fast, stateless engines. It has no shell quoting: paths with spaces and
 shell tricks cannot work. Use a small wrapper script if you need options.
@@ -133,17 +135,19 @@ Implemented on the Veskslop side (2026-09-15):
 - `tts` preferences carry `speed` (0.5–2.0) and `pitch` (-12–+12, semitones), both nullable.
 - `/api/audio/speak` and the MCP `speak` tool accept optional `speed` and `pitch` that override
   the preferences for that line.
-- The command provider substitutes `{speed}`/`{pitch}` and exports `VESKSLOP_TTS_SPEED` /
-  `VESKSLOP_TTS_PITCH` only when the value is set.
-- The HTTP provider adds `speed` and `pitch` to the request body only when set.
-- The TTS panel has speed and pitch sliders; changes are saved to the daemon preferences.
+- The command provider substitutes `{speed}`/`{pitch}`/`{expression}` and exports
+  `VESKSLOP_TTS_SPEED` / `VESKSLOP_TTS_PITCH` / `VESKSLOP_TTS_EXPRESSION` only when the value is set.
+- The HTTP provider adds `speed`, `pitch`, and `expression` to the request body only when set.
+- The TTS panel has speed presets, speed/pitch sliders, and an Expression slider that appears only
+  for voices that declare it (`expression` / `expression=NN` flags). Changes save to preferences.
 - Command mode advertises voices through `VESKSLOP_TTS_VOICES`. Entries are separated by commas or
   newlines and use `id`, `id|Name`, `id|Name|gender`, `id|Name|gender|language`, or
-  `id|Name|gender|language|flags`, where flags are `+`-separated. The `no-pitch` flag marks a voice
-  that ignores pitch; `/api/audio/tts/voices` then reports `supportsPitch: false` and the TTS panel
-  disables the pitch slider. While a custom command is set, the engine's declared voices replace
-  the espeak list, so no misleading espeak entries appear. Reading `/voices` for the HTTP provider
-  is still future work.
+  `id|Name|gender|language|flags`, where flags are `+`-separated. Flags: `no-pitch` (engine ignores
+  pitch) and `expression` / `expression=NN` (Flextalk profile parameter with its registry default).
+  `/api/audio/tts/voices` reports `supportsPitch` and `supportsExpression` /
+  `expressionDefault`; the TTS panel hides controls the voice does not support. While a custom
+  command is set, the engine's declared voices replace the espeak list. Reading `/voices` for the
+  HTTP provider is still future work.
 
 Do not encode settings into the voice string (for example `anna+speed1.2`). It breaks voice lists
 and is hard to validate.
@@ -290,6 +294,47 @@ host as `sapi4host -V <value>` and is not sent by Veskslop.
 - Not exposed by this integration: SSML, prosody/style tags, or SAPI4 attribute
   extensions beyond pitch/speed/volume.
 
+### Flextalk profile parameters (how to implement)
+
+Each Flextalk speaker has a profile the engine reads when the voice is loaded. It lives in
+the registry; **every numeric value must be `REG_DWORD`**:
+
+    HKLM\Software\AT&T\Watson\2.0\FlexTalk\2.0\Speakers\{11260610-C84A-11ce-AEC4-0000C0E9CB87}   # Keith Bell
+    HKLM\Software\AT&T\Watson\2.0\FlexTalk\2.0\Speakers\{000031CB-3699-551F-AED0-6B4893382D57}   # Kerry Watson
+
+| Value (REG_DWORD unless noted) | Keith Bell | Kerry Watson | Measured effect |
+| --- | --- | --- | --- |
+| Pitch | 27 | 65 | Natural pitch (F0); the same scale `ITTSAttributes` shifts at runtime |
+| Speaking Rate | 33 | 32 | Natural speech rate (about 150 wpm equivalent) |
+| Volume | 100 | 100 | Output gain; 0 = silence |
+| Expression | 59 | 100 | Audible; changes the waveform at equal duration |
+| Prominences | 17 | 17 | Audible; strong prosody/emphasis effect (F0 median 122 -> 197 Hz at 100) |
+| Head Size | 46 | 45 | Audible; brightness/level (peak 20001 -> 32205 at 100) |
+| Lowering | 40 | 40 | Audible but subtle |
+| Age | 30 | 30 | No measured effect on synthesis (informational) |
+| Gender (REG_SZ) | "" | "" | No measured effect on synthesis (informational) |
+| Mode Name / Speaker Name (REG_SZ) | "Keith Bell" | "Kerry Watson" | Mode name SAPI4 shows for the voice |
+
+How to apply a change:
+
+1. `setup/setup-flextalk.sh` writes these defaults, so re-running it restores them.
+2. Profiles are read at voice load. The host loads the engine per request, so the next
+   synthesis after a registry change uses the new profile; no engine restart is needed.
+3. Example (lower and slow Keith Bell), with `WINEPREFIX` pointing at the project prefix:
+
+       wine reg add 'HKLM\Software\AT&T\Watson\2.0\FlexTalk\2.0\Speakers\{11260610-C84A-11ce-AEC4-0000C0E9CB87}' \
+           /v Pitch /t REG_DWORD /d 20 /f
+       wine reg add '...' /v "Speaking Rate" /t REG_DWORD /d 28 /f
+
+   Never use `REG_SZ` for numeric values: the engine reads garbage and synthesizes a
+   monotone buzz at maximum pitch.
+4. Not exposed by the Veskslop contract (which sends only text/voice/speed/pitch). If
+   profile control is wanted later, the clean place is the wrapper: read an env var such
+   as `VESKSLOP_TTS_PROFILE` (`key=value` list or JSON), write the registry values before
+   synthesis, then restore. That keeps the Veskslop interface unchanged.
+5. Runtime `ITTSAttributes` pitch/speed/volume layer on top of the profile: the profile
+   defines the natural values, the attributes shift them per request.
+
 ### Transport and latency
 
 - Installation is one command: `setup/install.sh` (system dependencies with sudo, wine
@@ -363,13 +408,14 @@ _Added 2026-09-15._
   5–10 ms edge fades.
 - **Voice declarations**: list only usable IDs in `VESKSLOP_TTS_VOICES`. Veskslop hides the
   espeak list while a custom command is set, so a missing declaration means an empty voice list,
-  not a fallback. The list accepts commas or newlines, and the optional `no-pitch` flag tells the
-  UI to grey out the pitch slider for that voice.
-- **Flextalk pitch**: confirmed that pitch is a no-op for Keith Bell and Kerry Watson. Mark those
-  entries `no-pitch` so users are not offered a control that does nothing. Speed applies to every
-  voice and needs no flag.
-  _Engine correction (2026-09-15): the no-op was caused by the speaker registry values being
-  `REG_SZ`; with `REG_DWORD` pitch works and the voices are declared without the flag. See the
-  speed/pitch section._
+  not a fallback. The list accepts commas or newlines. Optional flags: `no-pitch` (hide the pitch
+  control) and `expression` / `expression=NN` (show the Expression slider and use NN as its
+  default).
+- **Flextalk pitch**: works now that the speaker registry values are `REG_DWORD`; no flag is
+  needed and Veskslop shows pitch for Keith Bell and Kerry Watson.
+- **Expression profile**: implemented for the Flextalk voices. Veskslop stores `tts.expression`
+  (0-100, nullable), sends it per line (`{expression}` / `VESKSLOP_TTS_EXPRESSION` / the HTTP body),
+  and shows the slider only for voices flagged `expression=NN`. A null value leaves the registry
+  untouched, so the voice keeps its engine default.
 - **Licensing**: keep the engine DLLs and voice data local and out of any repository; Veskslop
   never bundles or redistributes them.