# Stimulus types

VIPBench contains 9,800 voice pairs in **6 stimulus types**, designed to span the perceptual identity landscape from "obviously same" to "obviously different" with controlled ambiguous regions in between.

## The six types

| Type | Description | Metadata label | Pair count | P(same) shape |
|---|---|---|---|---|
| 1 | Same recording (reference compared with itself, segmented differently) | Same | 100 | concentrated near 1.0 |
| 2 | Same speaker, different recording | Same | 400 | high but spread |
| 3 | Same speaker, AI voice clone | Same | 400 | spreads across full range (clones with metadata-same label) |
| 4 | Different speakers, real recordings | Different | 400 | concentrated near 0.0 |
| 5 | Different speakers, AI voice clones | Different | 400 | concentrated near 0.0 |
| 6 | Continuously morphed voices | (no clean metadata label) | 8,100 | sweeps full range across the morph trajectory |

Total: **9,800 pairs**, of which 1,700 carry a clean metadata same/different label (Types 1-5) and 8,100 are morph trajectories.

Note: Type 6's 8,100 pairs are 81 stimuli per reference speaker x 100 reference speakers. The 81 stimuli per reference speaker decompose as 4 within-group comparison speakers (matched on sociophonetic group, age group, and gender) x 2 distinct recordings per comparison x 10 morph scales between 0 and 1, plus 1 shared anchor at scale 1 (4 x 2 x 10 + 1 = 81). Per-stimulus trajectory metadata is in `data/stimuli_interpol.csv`.

## Naming convention

Stimulus IDs in `data/stimuli.csv` and the audio filenames in `data/audio/comparison/` follow the pattern:

- **Types 1-5:** `<type>_<reference_speaker>` for type-1 same-recording pairs; `<type>_<reference_speaker><variant>` where the comparison clip varies across A-E for types 2-5.
  - Examples: `1_M01.wav` (Type 1, M01), `2_M01B.wav` (Type 2, M01 with variant B), `4_F03_F09B.wav` (Type 4, reference F03 paired with F09 variant B).
- **Type 6 morphs:** `6_<source_speaker><variant>_<target_speaker><variant>_<scale>.wav` where the variant letter (A-E) identifies the seed clip used for each speaker and `<scale>` is the interpolation level. Example: `6_M05A_M03A_065.wav` is a morph between M05's clip A and M03's clip A at scale 65.

The stimulus ID matches the comparison-audio basename (without `.wav`) and is the key into the embedding `.npz` files.

## Voice cloning

Voice clones (Types 3 and 5) were generated with Cartesia (a state-of-the-art TTS system) seeded from a natural source clip of the speaker being cloned. The variant letter in the stimulus ID identifies the seed: a Type 3 clone shares its seed clip with the comparison clip of the matched Type 2 pair, and a Type 5 clone shares its seed with the matched Type 4 pair. For example, `3_F01B` is seeded from the same F01B source clip that appears as the comparison in `2_F01B`; `5_M01_F09B` is seeded from the same F09B source clip that appears as the comparison in `4_M01_F09B`. The reference clip itself was not used as the seed. The clone shares the metadata identity of the source speaker by construction; whether listeners hear the clone as that speaker is the per-pair question that the benchmark measures via `P(same)`.

## Voice morphing

Type 6 pairs were generated using the voice-morphing feature of the same Cartesia TTS system, interpolating the latent voice representation of the reference speaker toward each of 4 within-group comparison speakers (matched on sociophonetic group, age group, and gender). For each reference speaker x comparison speaker x recording (2 distinct recordings per comparison speaker), 10 morph scales between 0 and 1 were sampled, plus 1 shared anchor at scale 1. Per reference speaker: 4 x 2 x 10 + 1 = 81 stimuli, totaling 8,100 across 100 reference speakers. Stimulus IDs encode the two endpoints and the scale (e.g., `6_M05A_M03A_065` = morph between M05 and M03 with seed recordings A from each, at scale 65). Morphs have no clean metadata speaker label: at scale 0 the audio matches one speaker, at scale 100 the other, and intermediate scales sweep a perceptual continuum. This is the largest category in the dataset (8,100 of 9,800 pairs) and is designed to probe identity perception at fine resolution. Per-stimulus trajectory metadata (source speakers, recording variants, scale) is in `data/stimuli_interpol.csv`.

## Why this design

The six types reflect three orthogonal axes:

1. **Metadata identity** (same vs different speaker): Types 1-2-3 vs 4-5; Type 6 sweeps.
2. **Synthesis** (real vs AI-generated): Types 1-2-4 vs 3-5; Type 6 is morphed.
3. **Ambiguity** (concentrated vs spread `P(same)`): Types 1, 4, 5 are concentrated; Types 3 and 6 sweep, exposing where listener perception diverges from the metadata label.

Types 3 and 6 are where perceptual and metadata identity most often disagree, making them the centerpiece of the benchmark's perception-vs-metadata contrast.