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> For a complete documentation index, see https://docs.nvidia.com/nemo/curator/v25.09/curate-audio/process-data/audio-analysis/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.nvidia.com/nemo/curator/_mcp/server.

# Audio Analysis

## Docs

- [Duration Calculation](https://docs.nvidia.com/nemo/curator/v25.09/curate-audio/process-data/audio-analysis/duration-calculation.md): Calculate precise audio duration using soundfile library for quality assessment and metadata generation
- [Audio Format Support](https://docs.nvidia.com/nemo/curator/v25.09/curate-audio/process-data/audio-analysis/format-validation.md): Audio format support and error handling in NeMo Curator audio processing stages


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> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.nvidia.com/nemo/curator/v25.09/curate-audio/process-data/audio-analysis/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.nvidia.com/nemo/curator/_mcp/server.

# Audio Analysis

> Extract and analyze audio file characteristics including duration calculation, format validation, and metadata extraction

Extract and analyze audio file characteristics for quality control, metadata generation, and dataset validation. Audio analysis provides essential information about audio files before and during processing.

## How It Works

Audio analysis in NeMo Curator examines audio files to extract:

1. **Duration Information**: Precise timing measurements using `soundfile`
2. **Format Characteristics**: Sample rate, bit depth, channels, and format
3. **Quality Indicators**: File integrity, format compliance, technical quality
4. **Metadata Extraction**: Embedded metadata and file properties

> **Note**
>
> NeMo Curator provides duration extraction as a built-in stage (`GetAudioDurationStage`). The format and metadata examples below show how to build custom stages and are not built-in.

## Input Requirements

Each audio data entry must include the path to the file:

```python
# Required key in each data item
{
    "audio_filepath": "/path/to/audio.wav"
}
```

Use `audio_filepath_key` to customize the key name when constructing `GetAudioDurationStage`.

## Duration Analysis

### Precise Duration Calculation

```python
from nemo_curator.stages.audio.common import GetAudioDurationStage

# Calculate audio duration for each file
duration_stage = GetAudioDurationStage(
    audio_filepath_key="audio_filepath",
    duration_key="duration"
)
```

The duration calculation:

* Uses the `soundfile` library; computes duration as frames ÷ sample rate
* Handles formats supported by `soundfile` (`libsndfile`)
* Returns -1.0 for corrupted or unreadable files
* Calculates: `duration = sample_count / sample_rate`

### Duration-Based Quality Assessment

After calculating durations, you can analyze the results:

### Duration Filtering Example

```python
from nemo_curator.stages.audio.common import PreserveByValueStage

# Keep samples between 1 and 15 seconds
min_duration_filter = PreserveByValueStage(
    input_value_key="duration",
    target_value=1.0,
    operator="ge"
)
max_duration_filter = PreserveByValueStage(
    input_value_key="duration",
    target_value=15.0,
    operator="le"
)
```

Refer to [Duration Filtering](/curate-audio/process-data/quality-assessment/duration-filtering) for end-to-end examples.

## Format Validation

NeMo Curator infers basic format validity during duration extraction using `soundfile.read`. If `soundfile`/`libsndfile` cannot read a file, `GetAudioDurationStage` sets `duration = -1.0`, which you can filter out. Refer to [Format Validation](/curate-audio/process-data/audio-analysis/format-validation) for behavior and supported formats.

### Basic Format Check

```python
import soundfile as sf

# Check if file is readable
try:
    info = sf.info("audio_file.wav")
    print(f"Duration: {info.duration}s, Sample rate: {info.samplerate}Hz")
except Exception as e:
    print(f"File validation failed: {e}")
```

## Complete Analysis Pipeline

Here is a complete working pipeline for audio analysis:

```python
from nemo_curator.pipeline import Pipeline
from nemo_curator.stages.audio.common import GetAudioDurationStage, PreserveByValueStage
from nemo_curator.stages.audio.inference.asr_nemo import InferenceAsrNemoStage

# Create analysis pipeline
pipeline = Pipeline(name="audio_analysis")

# 1. Calculate duration (handles format validation automatically)
pipeline.add_stage(GetAudioDurationStage(
    audio_filepath_key="audio_filepath",
    duration_key="duration"
))

# 2. Filter by duration (removes corrupted files with duration = -1.0)
pipeline.add_stage(PreserveByValueStage(
    input_value_key="duration",
    target_value=1.0,
    operator="ge"  # >= 1 second
))

pipeline.add_stage(PreserveByValueStage(
    input_value_key="duration", 
    target_value=15.0,
    operator="le"  # <= 15 seconds
))

# 3. Continue with ASR inference on validated files
pipeline.add_stage(InferenceAsrNemoStage(
    model_name="nvidia/stt_en_fastconformer_hybrid_large_pc"
))
```