Sentioscope

Speech and voice controls, as each vendor documents them

Runway: a sample, or a sentence describing a voice

Two routes sit side by side. A sample of ten seconds to five minutes, at most ten megabytes, or a description in words with a published minimum length rather than a maximum. The second route exists nowhere else in this register. As of 2026-09-22.

A recording, or a sentence with a floor under itThe sample route runs from ten seconds to five minutes at up to ten megabytes. The described route needs at least twenty characters, which is a floor rather than a ceiling and reads as a request for enough adjectives.From a sampleFrom a descriptionWhat is supplied10 s to 5 min of audio, under 10 MBAt least twenty characters of textWho has to existA performer who was recordedNobodyWhat is reproducibleThe clip, if it is keptThe sentence, if it is keptWhat you get to checkA preview once the voice is readyA preview once the voice is readyBoth become a stored voice addressed by its own id
Fig. 1 A described voice needs no performer and carries no identifiable person, which makes it the cheapest casting in this register.
Runway on voice source, statement by statement. Read from the vendor's custom voices reference on 2026-09-22.
What the documentation settlesWhat it leaves to a take
A custom voice can be built from a sample of 10 seconds to 5 minutes, at most 10 MBHow much of the read a five-minute sample carries that ten seconds does not
A voice can instead be described in words, with at least twenty charactersHow specific a description has to be to land where it was aimed
A voice is created asynchronously, reaches a ready state with a preview, then is used by idWhether a described voice is reproducible from the same sentence

Inclusion rule. Only statements found on the vendor page named in the caption, and only ones bearing on this one field. Nothing here is filled in from generated output. Order. In the order the statements arrive on the vendor's page.

1A minimum length on a description is a revealing constraint

Most published limits are ceilings. This one is a floor: the description has to run at least twenty characters. Read as engineering it stops empty strings; read as a hint it says the model wants enough adjectives to work with, and a three-word description will produce something generic.

The described route also steps around the consent question a sample carries, because there is no identifiable person behind a sentence about a voice. For a minor character nobody was going to record, that is the cheapest casting in this register.

2The sample window is the widest here, which changes the choice

Ten seconds to five minutes spans two different kinds of clip. At the short end this behaves like every other entry in the column, carrying timbre and little else. At five minutes there is room for range, and the choice of what to include becomes a directing decision rather than a technical one.

Nothing on the page says the longer clip produces a better voice, and it is worth not assuming so. A wide window means a production can experiment; it does not mean more audio is always better than a cleaner ten seconds.

3The other entry where a voice is built once and reused

One more entry constructs a voice before any shot and then addresses it by name. It publishes a threshold in minutes of studio time, where this one publishes a window and an alternative that needs no recording at all.

  • HeyGen — a recording to clone from.
  • Voice source
    A custom voice can be built from an audio sample between 10 seconds and 5 minutes long and at most 10 MBa published sample windowRunway, custom voices reference / recorded 2026-09-22
  • Voice source
    A voice can instead be asked for in words, with the description required to run at least 20 charactersa route that needs no recordingRunway, custom voices reference / recorded 2026-09-22
  • Per-character binding
    A voice is created asynchronously, reaches a ready state with a preview, and is then referred to by its own ida stored voice objectRunway, custom voices reference / recorded 2026-09-22

4Sources

Read from the custom voices reference at docs.dev.runwayml.com on 2026-09-22. The same column across every entry is on voice source; everything this vendor publishes about speech is on Runway. What counts as documented is on how read.