CHiME8 DASR NeMo Baseline Models

• The model files in this repository are the models used in this paper The CHiME-7 Challenge: System Description and Performance of NeMo Team’s DASR System.
• These models are needed to execute the CHiME8-DASR baseline CHiME8-DASR-Baseline NeMo
• VAD, Diarization and ASR models are all based on NVIDIA NeMo Conversational AI Toolkits.

1. Voice Activity Detection (VAD) Model:

MarbleNet_frame_VAD_chime7_Acrobat.nemo

• This model is based on NeMo MarbleNet VAD model.
• For validation, we use dataset comprises the CHiME-6 development subset as well as 50 hours of simulated audio data.
• The simulated data is generated using the NeMo multi-speaker data simulator on VoxCeleb1&2 datasets
• The multi-speaker data simulation results in a total of 2,000 hours of audio, of which approximately 30% is silence.
• The Model training incorporates SpecAugment and noise augmentation through MUSAN noise dataset.

2. Speaker Diarization Model: Multi-scale Diarization Decoder (MSDD-v2)

MSDD_v2_PALO_100ms_intrpl_3scales.nemo

• MSDD Reference: Park et al. (2022)
• MSDD-v2 speaker diarization system employs a multi-scale embedding approach and utilizes TitaNet speaker embedding extractor.
  • TitaNet Reference: Koluguri et al. (2022)
  • TitaNet Model is included in MSDD-v2 .nemo checkpoint file.
• Unlike the system that uses a multi-layer LSTM architecture, we employ a four-layer Transformer architecture with a hidden size of 384.
• This neural model generates logit values indicating speaker existence.
• Our diarization model is trained on approximately 3,000 hours of simulated audio mixture data from the same multi-speaker data simulator used in VAD model training, drawing from VoxCeleb1&2 and LibriSpeech datasets.
  • LibriSpeech Reference: OpenSLR Download,LibriSpeech, Panayotov et al. (2015)
• MUSAN noise is also used for adding additive background noise, focusing on music and broadband noise.

3. Automatic Speech Recognition (ASR) model

FastConformerXL-RNNT-chime7-GSS-finetuned.nemo

• This ASR model is based on NeMo FastConformer XL model.
• Single-channel audio generated using a multi-channel front-end (Guided Source Separation, GSS) is transcribed using a 0.6B parameter Conformer-based transducer (RNNT) model.
  • Model Reference: Gulati et al. (2020)
• The model was initialized using a publicly available NeMo checkpoint.
  • NeMo Checkpoint: NGC Model Card: Conformer Transducer XL
• This model was then fine-tuned on the CHiME-7 train and dev set, which includes the CHiME-6 and Mixer6 training subsets, after processing the data through the multi-channel ASR front-end, utilizing ground-truth diarization.
  • Fine-Tuning Details:
    • Fine-tuning Duration: 35,000 updates
    • Batch Size: 128

4. Language Model for ASR Decoding: KenLM Model

ASR_LM_chime7_only.kenlm

• This KenLM model is trained solely on CHiME7-DASR datasets (Mixer6, CHiME6, DipCo).
• We apply a word-piece level N-gram language model using byte-pair-encoding (BPE) tokens.
• This approach utilizes the SentencePiece and KenLM toolkits, based on the transcription of CHiME-7 train and dev sets.
  • SentencePiece: Kudo and Richardson (2018)
  • KenLM: KenLM GitRepo
• The token sets of our ASR and LM models were matched to ensure consistency.
• To combine several N-gram models with equal weights, we used the OpenGrm library.
  • OpenGrm: Roark et al. (2012)
• MAES decoding was employed for the transducer, which accelerates the decoding process.
  • MAES Decoding: Kim et al. (2020)
• As expected, integrating the beam-search decoder with the language model significantly enhances the performance of the end-to-end model compared to its pure counterpart.