diff --git a/README.md b/README.md
index 55c50f3d..95037029 100644
--- a/README.md
+++ b/README.md
@@ -28,7 +28,7 @@
 ----------
 
 The eSpeak NG (Next Generation) Text-to-Speech program is an open source speech
-synthesizer that supports [95 languages and accents](espeak-ng-data/voices/README.md).
+synthesizer that supports [95 languages and accents](docs/languages.md).
 It is based on the eSpeak engine created by Jonathan Duddington. It uses
 spectral formant synthesis by default which sounds robotic, but can be
 configured to use Klatt formant synthesis or MBROLA to give it a more natural
diff --git a/espeak-ng-data/voices/README.md b/docs/languages.md
similarity index 98%
rename from espeak-ng-data/voices/README.md
rename to docs/languages.md
index 6af28369..47203e61 100644
--- a/espeak-ng-data/voices/README.md
+++ b/docs/languages.md
@@ -1,8 +1,8 @@
-# Voices
+# Languages
 
-The voices in espeak-ng are grouped by their
+The languages in espeak-ng are grouped by their
 [ISO 639-5](https://en.wikipedia.org/wiki/List_of_ISO_639-5_codes) language
-family code. The voices are identified by their
+family code. They are identified by their
 [BCP 47](https://en.wikipedia.org/wiki/BCP47) identifier. For several accents
 and dialects,
 [private-use extensions](https://raw.githubusercontent.com/espeak-ng/bcp47-data/master/bcp47-extensions)
@@ -10,7 +10,7 @@ have been used.
 
 The supported languages are:
 
-| Family Code | Voice Identifier  | Language Family       | Language                    | Accent/Dialect         |
+| Family Code | Identifier        | Language Family       | Language                    | Accent/Dialect         |
 |-------------|-------------------|-----------------------|-----------------------------|------------------------|
 | `gmw`       | `af`              | West Germanic         | Afrikaans                   |                        |
 | `ine`       | `sq`              | Indo-European         | Albanian                    |                        |
diff --git a/docs/phonemes.md b/docs/phonemes.md
index 5d54ca91..343d063f 100644
--- a/docs/phonemes.md
+++ b/docs/phonemes.md
@@ -6,10 +6,14 @@
   - [Other Symbols](#other-symbols)
   - [Vowels](#vowels)
 - [Features](#features)
+  - [Air Flow](#air-flow)
+  - [Initiator](#initiator)
+  - [Phonation](#phonation)
+  - [Place of Articulation](#place-of-articulation)
+    - [Active Articulators](#active-articulators)
+    - [Passive Articulators](#passive-articulators)
   - [Consonants](#consonants)
-    - [Voicing](#voicing)
-    - [Place of Articulation](#place-of-articulation)
-      - [Co-articulation](#co-articulation)
+    - [Co-articulation](#co-articulation)
     - [Manner of Articulation](#manner-of-articulation)
   - [Vowels](#vowels-1)
     - [Height](#height)
@@ -19,7 +23,7 @@
     - [Syllabicity](#syllabicity)
     - [Consonant Release](#consonant-release)
       - [Gemination](#gemination)
-    - [Phonation](#phonation)
+    - [Fortis and Lenis](#fortis-and-lenis)
     - [Articulation](#articulation)
     - [Co-articulation](#co-articulation-1)
       - [Precomposed Characters](#precomposed-characters)
@@ -242,7 +246,7 @@ sections.
   </tr>
 </table>
 
-Symbols to the left are `vls`, and to the right are `vcd`.
+Symbols to the left have a `vls` phonation, and to the right have `mdv` phonation.
 
 ### Consonants (Non-Pulmonic)
 
@@ -290,7 +294,7 @@ Symbols to the left are `vls`, and to the right are `vcd`.
     <td> </td>
   </tr>
   <tr>
-    <th align="right"><code>vcd</code>&#xA0;<code>imp</code></th>
+    <th align="right"><code>mdv</code>&#xA0;<code>imp</code></th>
     <td>ɓ</td>
     <td> </td>
     <td> </td>
@@ -352,8 +356,8 @@ Symbols to the left are `vls`, and to the right are `vcd`.
 | Symbol | Features                |
 |--------|-------------------------|
 | ʍ      | `vls` `lbv` `apr`       |
-| w      | `vcd` `lbv` `apr`       |
-| ɥ      | `vcd` `lbp` `apr`       |
+| w      | `mdv` `lbv` `apr`       |
+| ɥ      | `mdv` `lbp` `apr`       |
 | ɧ      | `vls` `vzd` `pla` `frc` |
 
 ### Vowels
@@ -417,36 +421,105 @@ above table.
 
 ## Features
 
-### Consonants
+### Air Flow
 
-#### Voicing
+| Feature | Symbol | Name       | Description                                            |
+|---------|--------|------------|--------------------------------------------------------|
+| `egs`   | ↑      | egressive  | The air flow is moving outwards from the initiator.    |
+| `igs`   | ↓      | ingressive | The air flow is moving inwards towards the initiator.  |
 
-| Feature | Kirshenbaum | Name            |
-|---------|-------------|-----------------|
-| `vcd`   | `vcd`       | voiced          |
-| `vls`   | `vls`       | voiceless       |
+The ↑ and ↓ symbols are from the extended IPA<sup>\[<a href="#ref7">7</a>\]</sup>.
+They only need to be used when the air flow is different to the base IPA
+phoneme (e.g. using ↓ on pulmonic consonants).
 
-#### Place of Articulation
+### Initiator
 
-| Feature | Kirshenbaum | Name            |
-|---------|-------------|-----------------|
-| `blb`   | `blb`       | bilabial        |
-| `lbd`   | `lbd`       | labio-dental    |
-| `dnt`   | `dnt`       | dental          |
-| `alv`   | `alv`       | alveolar        |
-| `pla`   | `pla`       | post-alveolar (palato-alveolar) |
-| `rfx`   | `rfx`       | retroflex       |
-| `alp`   |             | alveolo-palatal |
-| `pal`   | `pal`       | palatal         |
-| `vel`   | `vel`       | velar           |
-| `uvl`   | `uvl`       | uvular          |
-| `phr`   | `phr`       | pharyngeal/epiglottal |
-| `glt`   | `glt`       | glottal         |
+| Feature | Name       | Description                                                           |
+|---------|------------|-----------------------------------------------------------------------|
+| `pmc`   | pulmonic   | The diaphragm and lungs are used to generate the airstream.           |
+| `gtc`   | glottalic  | The glottis is used to generate the airstream.                        |
+| `vlc`   | velaric    | The velum is closed and the tongue is used to generate the airstream. |
+| `pcv`   | percussive | There is no airstream used to produce this sound.                     |
+
+#### Phonation
+
+The phonation features describe the degree to which the glottis (vocal chords) are open or closed.
+
+| Feature | Symbol | Name            | Description                                                                 |
+|---------|--------|-----------------|-----------------------------------------------------------------------------|
+| `vls`   |        | voiceless       | The glottis is fully open, such that the vocal chords do not vibrate.       |
+| `brv`   | ◌̤      | breathy voice   | The glottis is closed slightly, to produce a whispered or murmured sound.   |
+| `slv`   | ◌̥      | slack voice     | The glottis is opened wider than `mdv`, but not enough to be `brv`.         |
+| `mdv`   |        | modal voice     | The glottis is opened to provide the optimal vibration of the vocal chords. |
+| `stv`   | ◌̬      | stiff voice     | The glottis is closed narrower than `mdv`, but not enough to be `crv`.      |
+| `crv`   | ◌̰      | creaky voice    | The glottis is closed to produce a vocal or glottal fry.                    |
+| `glc`   | ʔ͡◌    | glottal closure | The glottis is fully closed.                                                |
+
+The IPA ◌̥ diacritic is also used to fill the `vls` spaces in the IPA consonant
+charts. Thus, when ◌̥ is used with a `mdv` consonant that does not have an
+equivalent `vls` consonant, the resulting consonant is `vls`, not `slv`.
+
+### Place of Articulation
+
+The place of articulation is described in terms of an active articulator and
+one or more passive articulators<sup>\[<a href="#ref9">9</a>\]</sup>. The
+possible places of articulation are:
+
+| Place of Articulation | Feature   | Symbol | Active | Passive |
+|-----------------------|-----------|--------|--------|---------|
+| bilabial              | `blb`     |        | `lbl`  | `ulp`   |
+| labiodental           | `lbd`     | ◌̪      | `lbl`  | `utt`   |
+| dental                | `dnt`     | ◌̪      | `apc`  | `utt`   |
+| alveolar              | `alv`     |        | `apc`  | `alf`   |
+| palato-alveolar       | `pla`     |        | `lmn`  | `alb`   |
+| retroflex             | `rfx`     |        | `sac`  | `hpl`   |
+| alveolo-palatal       | `alp`     |        | `dsl`  | `alb`   |
+| palatal               | `pal`     |        | `dsl`  | `hpl`   |
+| velar                 | `vel`     |        | `dsl`  | `spl`   |
+| uvular                | `uvl`     |        | `dsl`  | `uvu`   |
+| pharyngeal            | `phr`     |        | `rdl`  | `prx`   |
+| glottal               | `glt`     |        | `lyx`  | `gts`   |
+
+The features for these places of articulation are provided for convenience, and
+to make it easier to describe the IPA consonants. Internally, the active and
+passive articulators are used.
+
+The ◌̪ diacritic is `lbd` when used on `blb` consonants, and `dnt` when used on
+`alv` consonants.
 
 __NOTE:__ The IPA charts make a distinction between pharyngeal and epiglottal
 consonants, but Wikipedia does not. This model uses the Wikipedia descriptions.
 
-##### Co-articulation
+#### Active Articulators
+
+| Feature | Name      | Articulator             |
+|---------|-----------|-------------------------|
+| `lbl`   | labial    | lower lip               |
+| `lmn`   | laminal   | tongue blade            |
+| `apc`   | apical    | tongue tip              |
+| `sac`   | subapical | underside of the tongue |
+| `dsl`   | dorsal    | tongue body             |
+| `rdl`   | radical   | tongue root             |
+| `lyx`   | laryngeal | larynx                  |
+
+#### Passive Articulators
+
+| Feature | Articulator            |
+|---------|------------------------|
+| `ulp`   | upper lip              |
+| `utt`   | upper teeth            |
+| `alf`   | alveolar ridge (front) |
+| `alb`   | alveolar ridge (back)  |
+| `hpl`   | hard palate            |
+| `spl`   | soft palate            |
+| `uvu`   | uvular                 |
+| `prx`   | pharynx                |
+| `egs`   | epiglottis             |
+| `gts`   | glottis                |
+
+### Consonants
+
+#### Co-articulation
 
 | Feature | Kirshenbaum | Name            |
 |---------|-------------|-----------------|
@@ -544,23 +617,13 @@ with the first phoneme using the `unx` feature. For example, n̚.n for a
 geminated n. This describes how with the `stp` and `nas` consonants, the
 mouth remains closed (`unx`) for the first of the geminated consonants.
 
-#### Phonation
+#### Fortis and Lenis
 
 | Feature | Kirshenbaum | IPA | Name            |
 |---------|-------------|-----|-----------------|
-| `brv`   |             | ◌̤   | breathy voiced  |
-| `crv`   |             | ◌̰   | creaky voiced   |
 | `fts`   |             | ◌͈   | fortis          |
 | `lns`   |             | ◌͉   | lenis           |
 
-The IPA ◌̬ and ◌̥ diacritics (*voiced* and *voiceless*) are used for both
-filling spaces in the IPA consonants chart and making the distinction
-between *fortis* and *lenis* consonants. Cainteoir Text-to-Speech uses `slv`
-(slack voice) and `stv` (stiff voice) for these diacritics. For eSpeak NG,
-these diacritics are only used for controlling their voiced/voiceless
-property (and thus their position on the IPA code chart), so `vls` and `vcd`
-are used for these diacritics.
-
 The extended IPA<sup>\[<a href="#ref7">7</a>\]</sup> ◌͈ and ◌͉ diacritics
 are used to specify lesser (`lns`) and greater (`fts`) oral pressure than
 the unmodified voiced or voiceless phoneme. This distinction is made by
@@ -574,7 +637,6 @@ the [length](#length) suprasegmentals are used instead.
 
 | Feature | Kirshenbaum | IPA | Name            |
 |---------|-------------|-----|-----------------|
-| `dzd`   |             | ◌̪   | dental          |
 | `apc`   |             | ◌̺   | apical          |
 | `lmn`   |             | ◌̻   | laminal         |
 | `lgl`   |             | ◌̼   | linguolabial    |
@@ -623,7 +685,7 @@ character.
 
 | Symbol | Features                      |
 |--------|-------------------------------|
-| ɫ      | `vcd` `fzd` `alv` `lat` `apr` |
+| ɫ      | `mdv` `fzd` `alv` `lat` `apr` |
 | ɚ      | `unr` `mid` `cnt` `rzd` `vwl` |
 | ɝ      | `unr` `lmd` `cnt` `rzd` `vwl` |
 
@@ -691,7 +753,7 @@ Appendix A of his ASCII/IPA transcription, but are not used in the rest of
 the specification.
 
 __NOTE:__ Evan Kirshenbaum transcribes ɦ as `h<?>` (`{mrm,glt,frc}`), while
-Wikipedia also lists this as a `{vcd,glt,frc}`<sup>\[<a href="#ref6">6</a>\]</sup>.
+Wikipedia also lists this as a `{mdv,glt,frc}`<sup>\[<a href="#ref6">6</a>\]</sup>.
 This is the only phoneme that Kirshenbaum uses the `mrm` feature for. As such,
 the `mrm` feature is not used within this document.
 
@@ -725,3 +787,7 @@ the `mrm` feature is not used within this document.
 8. <a name="ref8"></a> Wikipedia.
    [Fortis and lenis](https://en.wikipedia.org/wiki/Fortis_and_lenis). 2017,
    Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA).
+
+9. <a name="ref9"></a> Wikipedia.
+   [Place of articulation](https://en.wikipedia.org/wiki/Place_of_articulation). 2017,
+   Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA).