Benchmark wav

This example measuers the performance of loading WAV audio.

It compares three different approaches for loading WAV files:

• spdl.io.load_wav(): Fast native WAV parser optimized for simple PCM formats

• spdl.io.load_audio(): General-purpose audio loader using FFmpeg backend

• soundfile (libsndfile): Popular third-party audio I/O library

The benchmark suite evaluates performance across multiple dimensions:

• Various audio configurations (sample rates, channels, bit depths, durations)

• Different thread counts (1, 2, 4, 8, 16) to measure parallel scaling

• Statistical analysis with 95% confidence intervals using Student’s t-distribution

• Queries per second (QPS) as the primary performance metric

Example

$ numactl --membind 0 --cpubind 0 python benchmark_wav.py --output wav_benchmark_results.csv
# Plot results
$ python benchmark_wav_plot.py --input wav_benchmark_results.csv --output wav_benchmark_plot.png
# Plot results without load_wav
$ python benchmark_wav_plot.py --input wav_benchmark_results.csv --output wav_benchmark_plot_2.png --filter '3. spdl.io.load_wav'

Result

The following plot shows the QPS (measured by the number of files processed) of each functions with different audio durations.

The spdl.io.load_wav() is a lot faster than the others, because all it does is reinterpret the input byte string as array. It shows the same performance for audio with longer duration.

And since parsing WAV is instant, the spdl.io.load_wav function spends more time on creation of NumPy Array. It needs to acquire the GIL, thus the performance does not scale in multi-threading. (This performance pattern of this function is pretty same as the spdl.io.load_npz.)

The following is the same plot without load_wav.

libsoundfile has to process data iteratively (using io.BytesIO) because it does not support directly loading from byte string, so it takes longer to process longer audio data. The performance trend (single thread being the fastest) suggests that it does not release the GIL majority of the time.

The spdl.io.load_audio() function (the generic FFmpeg-based implementation) does a lot of work so its overall performance is not as good, but it scales in multi-threading as it releases the GIL almost entirely.

Free-threaded Python

The cases above where multi-threading does not help are caused by contention on the GIL — most visibly soundfile, which holds the GIL for most of its work, so a single thread ends up being the fastest. This contention disappears on a free-threaded (no-GIL) build of Python (e.g. 3.14t). The following is the same benchmark run on 3.14t.

Without the GIL, soundfile now scales with the number of threads instead of slowing down, improving its throughput at 16 threads by more than an order of magnitude. spdl.io.load_audio(), which already releases the GIL, is essentially unchanged.

The numbers from both runs are tabulated below.

Soundfile

Duration	1s		10s		60s
Build	3.14	3.14t	3.14	3.14t	3.14	3.14t
1	9,904	11,910	5,864	6,500	1,869	2,054
2	5,481	19,120	4,188	10,645	1,481	3,599
4	3,142	30,447	2,491	16,438	1,201	6,280
8	2,375	45,220	1,993	25,208	1,163	10,725
16	2,643	54,900	2,121	40,948	1,017	14,103

spdl.io.load_audio

Duration	1s		10s		60s
Build	3.14	3.14t	3.14	3.14t	3.14	3.14t
1	116	119	43	45	38	38
2	258	271	85	88	74	75
4	512	511	168	176	144	152
8	1,011	1,035	337	352	286	296
16	1,915	2,012	652	698	538	574

spdl.io.load_wav

Duration	1s		10s		60s
Build	3.14	3.14t	3.14	3.14t	3.14	3.14t
1	51,585	79,572	47,905	107,119	49,404	76,757
2	49,882	98,500	49,057	97,641	45,787	98,364
4	51,084	87,790	49,228	91,243	50,026	94,748
8	48,710	77,335	49,124	73,603	47,977	76,574
16	38,366	65,094	37,587	62,512	38,210	63,498

Source

Source

Click here to see the source.

# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the BSD-style license found in the
# LICENSE file in the root directory of this source tree.


"""This example measuers the performance of loading WAV audio.

It compares three different approaches for loading WAV files:

- :py:func:`spdl.io.load_wav`: Fast native WAV parser optimized for simple PCM formats
- :py:func:`spdl.io.load_audio`: General-purpose audio loader using FFmpeg backend
- ``soundfile`` (``libsndfile``): Popular third-party audio I/O library

The benchmark suite evaluates performance across multiple dimensions:

- Various audio configurations (sample rates, channels, bit depths, durations)
- Different thread counts (1, 2, 4, 8, 16) to measure parallel scaling
- Statistical analysis with 95% confidence intervals using Student's t-distribution
- Queries per second (QPS) as the primary performance metric

**Example**

.. code-block:: shell

   $ numactl --membind 0 --cpubind 0 python benchmark_wav.py --output wav_benchmark_results.csv
   # Plot results
   $ python benchmark_wav_plot.py --input wav_benchmark_results.csv --output wav_benchmark_plot.png
   # Plot results without load_wav
   $ python benchmark_wav_plot.py --input wav_benchmark_results.csv --output wav_benchmark_plot_2.png --filter '3. spdl.io.load_wav'

**Result**

The following plot shows the QPS (measured by the number of files processed) of each
functions with different audio durations.

.. image:: ../../_static/data/example-benchmark-wav.webp


The :py:func:`spdl.io.load_wav` is a lot faster than the others, because all it
does is reinterpret the input byte string as array.
It shows the same performance for audio with longer duration.

And since parsing WAV is instant, the spdl.io.load_wav function spends more time on
creation of NumPy Array.
It needs to acquire the GIL, thus the performance does not scale in multi-threading.
(This performance pattern of this function is pretty same as the
:ref:`spdl.io.load_npz <example-benchmark-numpy>`.)

The following is the same plot without ``load_wav``.

.. image:: ../../_static/data/example-benchmark-wav-2.webp

``libsoundfile`` has to process data iteratively (using ``io.BytesIO``) because
it does not support directly loading from byte string, so it takes longer to process
longer audio data.
The performance trend (single thread being the fastest) suggests that
it does not release the GIL majority of the time.

The :py:func:`spdl.io.load_audio` function (the generic FFmpeg-based implementation) does
a lot of work so its overall performance is not as good,
but it scales in multi-threading as it releases the GIL almost entirely.

**Free-threaded Python**

The cases above where multi-threading does not help are caused by contention on
the GIL — most visibly ``soundfile``, which holds the GIL for most of its work,
so a single thread ends up being the fastest. This contention disappears on a
free-threaded (no-GIL) build of Python (e.g. ``3.14t``). The following is the
same benchmark run on ``3.14t``.

.. image:: ../../_static/data/example-benchmark-wav-freethreading.png

Without the GIL, ``soundfile`` now scales with the number of threads instead of
slowing down, improving its throughput at 16 threads by more than an order of
magnitude. :py:func:`spdl.io.load_audio`, which already releases the GIL, is
essentially unchanged.

The numbers from both runs are tabulated below.

**Soundfile**

+----------+--------+---------+--------+--------+--------+---------+
| Duration |       1s         |       10s       |       60s        |
+----------+--------+---------+--------+--------+--------+---------+
|  Build   |  3.14  |   3.14t |   3.14 |  3.14t |  3.14  |   3.14t |
+==========+========+=========+========+========+========+=========+
|        1 |  9,904 |  11,910 |  5,864 |  6,500 |  1,869 |   2,054 |
+----------+--------+---------+--------+--------+--------+---------+
|        2 |  5,481 |  19,120 |  4,188 | 10,645 |  1,481 |   3,599 |
+----------+--------+---------+--------+--------+--------+---------+
|        4 |  3,142 |  30,447 |  2,491 | 16,438 |  1,201 |   6,280 |
+----------+--------+---------+--------+--------+--------+---------+
|        8 |  2,375 |  45,220 |  1,993 | 25,208 |  1,163 |  10,725 |
+----------+--------+---------+--------+--------+--------+---------+
|       16 |  2,643 |  54,900 |  2,121 | 40,948 |  1,017 |  14,103 |
+----------+--------+---------+--------+--------+--------+---------+


**spdl.io.load_audio**

+----------+--------+---------+--------+--------+--------+---------+
| Duration |       1s         |       10s       |       60s        |
+----------+--------+---------+--------+--------+--------+---------+
|  Build   |  3.14  |   3.14t |   3.14 |  3.14t |  3.14  |   3.14t |
+==========+========+=========+========+========+========+=========+
|        1 |    116 |     119 |     43 |     45 |     38 |      38 |
+----------+--------+---------+--------+--------+--------+---------+
|        2 |    258 |     271 |     85 |     88 |     74 |      75 |
+----------+--------+---------+--------+--------+--------+---------+
|        4 |    512 |     511 |    168 |    176 |    144 |     152 |
+----------+--------+---------+--------+--------+--------+---------+
|        8 |  1,011 |   1,035 |    337 |    352 |    286 |     296 |
+----------+--------+---------+--------+--------+--------+---------+
|       16 |  1,915 |   2,012 |    652 |    698 |    538 |     574 |
+----------+--------+---------+--------+--------+--------+---------+

**spdl.io.load_wav**

+----------+--------+--------+--------+---------+--------+--------+
| Duration |       1s        |       10s        |       60s       |
+----------+--------+--------+--------+---------+--------+--------+
|  Build   |  3.14  |  3.14t |   3.14 |   3.14t |  3.14  |  3.14t |
+==========+========+========+========+=========+========+========+
|        1 | 51,585 | 79,572 | 47,905 | 107,119 | 49,404 | 76,757 |
+----------+--------+--------+--------+---------+--------+--------+
|        2 | 49,882 | 98,500 | 49,057 |  97,641 | 45,787 | 98,364 |
+----------+--------+--------+--------+---------+--------+--------+
|        4 | 51,084 | 87,790 | 49,228 |  91,243 | 50,026 | 94,748 |
+----------+--------+--------+--------+---------+--------+--------+
|        8 | 48,710 | 77,335 | 49,124 |  73,603 | 47,977 | 76,574 |
+----------+--------+--------+--------+---------+--------+--------+
|       16 | 38,366 | 65,094 | 37,587 |  62,512 | 38,210 | 63,498 |
+----------+--------+--------+--------+---------+--------+--------+


"""

__all__ = [
    "BenchmarkConfig",
    "create_wav_data",
    "load_sf",
    "load_spdl_audio",
    "load_spdl_wav",
    "main",
]

import argparse
import io
import os
from collections.abc import Callable
from dataclasses import dataclass

import numpy as np
import scipy.io.wavfile
import soundfile as sf
import spdl.io
from numpy.typing import NDArray

try:
    from examples.benchmark_utils import (  # pyre-ignore[21]
        BenchmarkResult,
        BenchmarkRunner,
        ExecutorType,
        get_default_result_path,
        save_results_to_csv,
    )
except ImportError:
    from spdl.examples.benchmark_utils import (
        BenchmarkResult,
        BenchmarkRunner,
        ExecutorType,
        get_default_result_path,
        save_results_to_csv,
    )


DEFAULT_RESULT_PATH: str = get_default_result_path(__file__)


@dataclass(frozen=True)
class BenchmarkConfig:
    """BenchmarkConfig()

    Configuration for a single WAV benchmark run.

    Combines both audio file parameters and benchmark execution parameters.
    """

    function_name: str
    """Name of the function being tested"""

    function: Callable[[bytes], NDArray]
    """The actual function to benchmark"""

    sample_rate: int
    """Audio sample rate in Hz"""

    num_channels: int
    """Number of audio channels"""

    bits_per_sample: int
    """Bit depth per sample (16 or 32)"""

    duration_seconds: float
    """Duration of the audio file in seconds"""

    num_threads: int
    """Number of concurrent threads"""

    iterations: int
    """Number of iterations per run"""

    num_runs: int
    """Number of runs for statistical analysis"""


def create_wav_data(
    sample_rate: int = 44100,
    num_channels: int = 2,
    bits_per_sample: int = 16,
    duration_seconds: float = 1.0,
) -> tuple[bytes, NDArray]:
    """Create a WAV file in memory for benchmarking.

    Args:
        sample_rate: Sample rate in Hz
        num_channels: Number of audio channels
        bits_per_sample: Bits per sample (16 or 32)
        duration_seconds: Duration of audio in seconds

    Returns:
        Tuple of (WAV file as bytes, audio samples array)
    """
    num_samples = int(sample_rate * duration_seconds)

    dtype_map = {
        16: np.int16,
        32: np.int32,
    }
    dtype = dtype_map[bits_per_sample]
    max_amplitude = 32767 if bits_per_sample == 16 else 2147483647

    t = np.linspace(0, duration_seconds, num_samples)
    frequencies = np.asarray(440.0 + np.arange(num_channels) * 110.0)
    sine_waves = np.sin(2 * np.pi * frequencies[:, np.newaxis] * t)
    samples = (sine_waves.T * max_amplitude).astype(dtype)

    wav_buffer = io.BytesIO()
    scipy.io.wavfile.write(wav_buffer, sample_rate, samples)
    wav_data = wav_buffer.getvalue()

    return wav_data, samples


def load_sf(wav_data: bytes) -> NDArray:
    """Load WAV data using soundfile library.

    Args:
        wav_data: WAV file data as bytes

    Returns:
        Audio samples array as int16 numpy array
    """
    audio_file = io.BytesIO(wav_data)
    data, _ = sf.read(audio_file, dtype="int16")
    return data


def load_spdl_audio(wav_data: bytes) -> NDArray:
    """Load WAV data using :py:func:`spdl.io.load_audio` function.

    Args:
        wav_data: WAV file data as bytes

    Returns:
        Audio samples array as numpy array
    """
    return spdl.io.to_numpy(spdl.io.load_audio(wav_data, filter_desc=None))


def load_spdl_wav(wav_data: bytes) -> NDArray:
    """Load WAV data using :py:func:`spdl.io.load_wav` function.

    Args:
        wav_data: WAV file data as bytes

    Returns:
        Audio samples array as numpy array
    """
    return spdl.io.to_numpy(spdl.io.load_wav(wav_data))


def _parse_args() -> argparse.Namespace:
    """Parse command line arguments for the benchmark script.

    Returns:
        Parsed command line arguments
    """
    parser = argparse.ArgumentParser(description="Benchmark WAV loading performance")
    parser.add_argument(
        "--output",
        type=lambda p: os.path.realpath(p),
        default=DEFAULT_RESULT_PATH,
        help="Output file path.",
    )
    return parser.parse_args()


def main() -> None:
    """Run comprehensive benchmark suite for WAV loading performance.

    Benchmarks multiple configurations of audio files with different durations,
    comparing spdl.io.load_wav, spdl.io.load_audio, and soundfile libraries
    across various thread counts (1, 2, 4, 8, 16).
    """
    args = _parse_args()

    # Define audio configurations to test
    audio_configs = [
        # (sample_rate, num_channels, bits_per_sample, duration_seconds)
        # (8000, 1, 16, 1.0),  # Low quality mono
        # (16000, 1, 16, 1.0),  # Speech quality mono
        # (48000, 2, 16, 1.0),  # High quality stereo
        # (48000, 8, 16, 1.0),  # Multi-channel audio
        (44100, 2, 16, 1.0),  # CD quality stereo
        (44100, 2, 16, 10.0),  #
        (44100, 2, 16, 60.0),  #
        # (44100, 2, 24, 1.0),  # 24-bit audio
    ]

    thread_counts = [1, 2, 4, 8, 16]

    # Define benchmark function configurations
    # (function_name, function, iterations_multiplier, num_runs)
    benchmark_functions = [
        ("3. spdl.io.load_wav", load_spdl_wav, 100, 100),  # Fast but unstable
        ("2. spdl.io.load_audio", load_spdl_audio, 10, 5),  # Slower but stable
        ("1. soundfile", load_sf, 10, 5),  # Slower but stable
    ]

    results: list[BenchmarkResult[BenchmarkConfig]] = []

    for sample_rate, num_channels, bits_per_sample, duration_seconds in audio_configs:
        # Create WAV data for this audio configuration
        wav_data, ref = create_wav_data(
            sample_rate=sample_rate,
            num_channels=num_channels,
            bits_per_sample=bits_per_sample,
            duration_seconds=duration_seconds,
        )

        print(
            f"\n{sample_rate}Hz, {num_channels}ch, {bits_per_sample}bit, {duration_seconds}s"
        )
        print(
            f"Threads,"
            f"SPDL WAV QPS ({duration_seconds} sec),CI Lower,CI Upper,"
            f"SPDL Audio QPS ({duration_seconds} sec),CI Lower,CI Upper,"
            f"soundfile QPS ({duration_seconds} sec),CI Lower,CI Upper"
        )

        for num_threads in thread_counts:
            thread_results: list[BenchmarkResult[BenchmarkConfig]] = []

            with BenchmarkRunner(
                executor_type=ExecutorType.THREAD,
                num_workers=num_threads,
            ) as runner:
                for (
                    function_name,
                    function,
                    iterations_multiplier,
                    num_runs,
                ) in benchmark_functions:
                    config = BenchmarkConfig(
                        function_name=function_name,
                        function=function,
                        sample_rate=sample_rate,
                        num_channels=num_channels,
                        bits_per_sample=bits_per_sample,
                        duration_seconds=duration_seconds,
                        num_threads=num_threads,
                        iterations=iterations_multiplier * num_threads,
                        num_runs=num_runs,
                    )

                    result, output = runner.run(
                        config,
                        lambda fn=function, data=wav_data: fn(data),
                        config.iterations,
                        num_runs=config.num_runs,
                    )

                    output_to_validate = output
                    if output_to_validate.ndim == 1:
                        output_to_validate = output_to_validate[:, None]
                    np.testing.assert_array_equal(output_to_validate, ref)

                    thread_results.append(result)
                    results.append(result)

            # Print results for this thread count (all 3 benchmarks)
            spdl_wav_result = thread_results[0]
            spdl_audio_result = thread_results[1]
            soundfile_result = thread_results[2]
            print(
                f"{num_threads},"
                f"{spdl_wav_result.qps:.2f},{spdl_wav_result.ci_lower:.2f},{spdl_wav_result.ci_upper:.2f},"
                f"{spdl_audio_result.qps:.2f},{spdl_audio_result.ci_lower:.2f},{spdl_audio_result.ci_upper:.2f},"
                f"{soundfile_result.qps:.2f},{soundfile_result.ci_lower:.2f},{soundfile_result.ci_upper:.2f}"
            )

    save_results_to_csv(results, args.output)
    print(
        f"\nBenchmark complete. To generate plots, run:\n"
        f"python benchmark_wav_plot.py --input {args.output} "
        f"--output {args.output.replace('.csv', '.png')}"
    )


if __name__ == "__main__":
    main()

API Reference

Functions

create_wav_data(sample_rate: int = 44100, num_channels: int = 2, bits_per_sample: int = 16, duration_seconds: float = 1.0) → tuple[bytes, NDArray]

Create a WAV file in memory for benchmarking.

Parameters:

• sample_rate – Sample rate in Hz

• num_channels – Number of audio channels

• bits_per_sample – Bits per sample (16 or 32)

• duration_seconds – Duration of audio in seconds

Returns:

Tuple of (WAV file as bytes, audio samples array)

load_sf(wav_data: bytes) → NDArray

Load WAV data using soundfile library.

Parameters:

wav_data – WAV file data as bytes

Returns:

Audio samples array as int16 numpy array

load_spdl_audio(wav_data: bytes) → NDArray

Load WAV data using spdl.io.load_audio() function.

Parameters:

wav_data – WAV file data as bytes

Returns:

Audio samples array as numpy array

load_spdl_wav(wav_data: bytes) → NDArray

Load WAV data using spdl.io.load_wav() function.

Parameters:

wav_data – WAV file data as bytes

Returns:

Audio samples array as numpy array

main() → None

Run comprehensive benchmark suite for WAV loading performance.

Benchmarks multiple configurations of audio files with different durations, comparing spdl.io.load_wav, spdl.io.load_audio, and soundfile libraries across various thread counts (1, 2, 4, 8, 16).

Classes

class BenchmarkConfig

Configuration for a single WAV benchmark run.

Combines both audio file parameters and benchmark execution parameters.

bits_per_sample: int

Bit depth per sample (16 or 32)

duration_seconds: float

Duration of the audio file in seconds

function: Callable[[bytes], NDArray]

The actual function to benchmark

function_name: str

Name of the function being tested

iterations: int

Number of iterations per run

num_channels: int

Number of audio channels

num_runs: int

Number of runs for statistical analysis

num_threads: int

Number of concurrent threads

sample_rate: int

Audio sample rate in Hz