whisper : improve beam search candidate diversity #1947
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As of ggml-org#1486, whisper.cpp uses a unified KV cache with KQ masking. As a result, depending on their location in the batch, identical sequences in a batch can have slightly different outputs due to floating point rounding errors during reduction. See the discussion in ggml-org#1941 for more details. The beam search code used "has identical sum of log probabilities" as a shorthand for "is an identical token sequence". However, per above, identical tokens do not necessarily result in identical probabilities. Instead, explicitly compare on sequences. This is linear in cost when they are identical, but the lengths are always small and the comparisons are cheap. This increases diversity during beam search. This improves output quality for some short samples I've been working with, at no detectable performance cost. I haven't checked against larger corpuses. Fixes ggml-org#1941
ggerganov
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Mar 10, 2024
jiahansu
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Apr 17, 2024
As of ggml-org#1486, whisper.cpp uses a unified KV cache with KQ masking. As a result, depending on their location in the batch, identical sequences in a batch can have slightly different outputs due to floating point rounding errors during reduction. See the discussion in ggml-org#1941 for more details. The beam search code used "has identical sum of log probabilities" as a shorthand for "is an identical token sequence". However, per above, identical tokens do not necessarily result in identical probabilities. Instead, explicitly compare on sequences. This is linear in cost when they are identical, but the lengths are always small and the comparisons are cheap. This increases diversity during beam search. This improves output quality for some short samples I've been working with, at no detectable performance cost. I haven't checked against larger corpuses. Fixes ggml-org#1941
viktor-silakov
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May 11, 2024
As of ggml-org#1486, whisper.cpp uses a unified KV cache with KQ masking. As a result, depending on their location in the batch, identical sequences in a batch can have slightly different outputs due to floating point rounding errors during reduction. See the discussion in ggml-org#1941 for more details. The beam search code used "has identical sum of log probabilities" as a shorthand for "is an identical token sequence". However, per above, identical tokens do not necessarily result in identical probabilities. Instead, explicitly compare on sequences. This is linear in cost when they are identical, but the lengths are always small and the comparisons are cheap. This increases diversity during beam search. This improves output quality for some short samples I've been working with, at no detectable performance cost. I haven't checked against larger corpuses. Fixes ggml-org#1941
iThalay
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Sep 23, 2024
As of ggml-org#1486, whisper.cpp uses a unified KV cache with KQ masking. As a result, depending on their location in the batch, identical sequences in a batch can have slightly different outputs due to floating point rounding errors during reduction. See the discussion in ggml-org#1941 for more details. The beam search code used "has identical sum of log probabilities" as a shorthand for "is an identical token sequence". However, per above, identical tokens do not necessarily result in identical probabilities. Instead, explicitly compare on sequences. This is linear in cost when they are identical, but the lengths are always small and the comparisons are cheap. This increases diversity during beam search. This improves output quality for some short samples I've been working with, at no detectable performance cost. I haven't checked against larger corpuses. Fixes ggml-org#1941
iThalay
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to iThalay/whisper.cpp
that referenced
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Sep 23, 2024
As of ggml-org#1486, whisper.cpp uses a unified KV cache with KQ masking. As a result, depending on their location in the batch, identical sequences in a batch can have slightly different outputs due to floating point rounding errors during reduction. See the discussion in ggml-org#1941 for more details. The beam search code used "has identical sum of log probabilities" as a shorthand for "is an identical token sequence". However, per above, identical tokens do not necessarily result in identical probabilities. Instead, explicitly compare on sequences. This is linear in cost when they are identical, but the lengths are always small and the comparisons are cheap. This increases diversity during beam search. This improves output quality for some short samples I've been working with, at no detectable performance cost. I haven't checked against larger corpuses. Fixes ggml-org#1941
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As of #1486, whisper.cpp uses a unified KV cache with KQ masking.
As a result, depending on their location in the batch,
identical sequences in a batch can have slightly different outputs
due to floating point rounding errors during reduction.
See the discussion in #1941 for more details.
The beam search code used "has identical sum of log probabilities"
as a shorthand for "is an identical token sequence". However, per above,
identical tokens do not necessarily result in identical probabilities.
Instead, explicitly compare on sequences.
This is linear in cost when they are identical,
but the lengths are always small and the comparisons are cheap.
This increases diversity during beam search.
This improves output quality for some short samples I've been working
with, at no detectable performance cost.
I haven't checked against larger corpuses.
Fixes #1941