tests/collections/audio/test_audio_modules_transforms.py

# Copyright (c) 2022, NVIDIA CORPORATION.  All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
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# See the License for the specific language governing permissions and
# limitations under the License.

import importlib

import numpy as np
import pytest
import torch
from einops import rearrange

from nemo.collections.audio.modules.transforms import AudioToSpectrogram, SpectrogramToAudio


class TestAudioSpectrogram:
    @pytest.mark.unit
    @pytest.mark.parametrize('fft_length', [64, 512])
    @pytest.mark.parametrize('num_channels', [1, 3])
    def test_audio_to_spec(self, fft_length: int, num_channels: int):
        """Test output length for audio to spectrogram.

        Create signals of arbitrary length and check output
        length is matching the actual transform length.
        """
        hop_lengths = [fft_length // 2, fft_length // 3, fft_length // 4]
        batch_size = 4
        num_examples = 20
        random_seed = 42
        atol = 1e-6

        _rng = np.random.default_rng(seed=random_seed)

        for n in range(num_examples):

            # Generate time-domain examples with different length
            input_length = _rng.integers(low=fft_length, high=100 * fft_length, size=batch_size)  # in samples
            x = _rng.normal(size=(batch_size, num_channels, np.max(input_length)))
            x = torch.tensor(x)
            for b in range(batch_size):
                x[b, :, input_length[b] :] = 0

            for hop_length in hop_lengths:
                # Prepare transform
                audio2spec = AudioToSpectrogram(fft_length=fft_length, hop_length=hop_length)

                # Transform the whole batch
                batch_spec, batch_spec_len = audio2spec(input=x, input_length=torch.tensor(input_length))

                for b in range(batch_size):

                    # Transform just the current example
                    b_spec, b_spec_len = audio2spec(input=x[b : b + 1, :, : input_length[b]])
                    actual_len = b_spec.size(-1)

                    # Check lengths
                    assert (
                        actual_len == b_spec_len
                    ), f'Output length not matching for example ({n}, {b}) with length {input_length[n]} (hop_length={hop_length}): true {actual_len} vs calculated {b_spec_len}.'

                    assert (
                        actual_len == batch_spec_len[b]
                    ), f'Output length not matching for example ({n}, {b}) with length {input_length[n]} (hop_length={hop_length}): true {actual_len} vs calculated batch len {batch_spec_len[b]}.'

                    # Make sure transforming a batch is the same as transforming individual examples
                    assert torch.allclose(
                        batch_spec[b, ..., :actual_len], b_spec, atol=atol
                    ), f'Spectrograms not matching for example ({n}, {b}) with length {input_length[b]} (hop_length={hop_length})'

    @pytest.mark.unit
    @pytest.mark.parametrize('fft_length', [64, 512])
    @pytest.mark.parametrize('num_channels', [1, 3])
    def test_spec_to_audio(self, fft_length: int, num_channels: int):
        """Test output length for spectrogram to audio.

        Create signals of arbitrary length and check output
        length is matching the actual transform length.
        """
        hop_lengths = [fft_length // 2, fft_length // 3, fft_length // 4]
        batch_size = 4
        num_examples = 20
        random_seed = 42
        atol = 1e-6

        _rng = np.random.default_rng(seed=random_seed)

        for n in range(num_examples):

            # Generate spectrogram examples with different lengths
            input_length = _rng.integers(low=10, high=100, size=batch_size)  # in frames
            input_shape = (batch_size, num_channels, fft_length // 2 + 1, np.max(input_length))
            spec = _rng.normal(size=input_shape) + 1j * _rng.normal(size=input_shape)
            spec = torch.tensor(spec)
            spec[..., 0, :] = spec[..., 0, :].real
            spec[..., -1, :] = spec[..., -1, :].real
            for b in range(batch_size):
                spec[b, ..., input_length[b] :] = 0

            for hop_length in hop_lengths:
                # Prepare transform
                spec2audio = SpectrogramToAudio(fft_length=fft_length, hop_length=hop_length)

                # Transform the whole batch
                batch_x, batch_x_len = spec2audio(input=spec, input_length=torch.tensor(input_length))

                for b in range(batch_size):

                    # Transform just the current example
                    b_x, b_x_len = spec2audio(input=spec[b : b + 1, ..., : input_length[b]])

                    actual_len = b_x.size(-1)

                    # Check lengths
                    assert (
                        b_x_len == actual_len
                    ), f'Output length not matching for example ({n}, {b}) with {input_length[b]} frames (hop_length={hop_length}): true {actual_len} vs calculated {b_x_len}.'

                    assert (
                        batch_x_len[b] == actual_len
                    ), f'Output length not matching for example ({n}, {b}) with {input_length[b]} frames (hop_length={hop_length}): true {actual_len} vs calculated batch {batch_x_len[b]}.'

                    # Make sure transforming a batch is the same as transforming individual examples
                    if input_length[b] < spec.size(-1):
                        # Discard the last bit of the signal which differs due to number of frames in batch (with zero padded frames) vs individual (only valid frames).
                        # The reason for this difference is normalization with `window_sumsquare` of the inverse STFT. More specifically,
                        # batched and non-batched transform are using on a different number of frames.
                        tail_length = max(fft_length // 2 - hop_length, 0)
                    else:
                        tail_length = 0
                    valid_len = actual_len - tail_length
                    batch_x_valid = batch_x[b, :, :valid_len]
                    b_x_valid = b_x[..., :valid_len]
                    assert torch.allclose(
                        batch_x_valid, b_x_valid, atol=atol
                    ), f'Signals not matching for example ({n}, {b}) with length {input_length[b]} (hop_length={hop_length}): max abs diff {torch.max(torch.abs(batch_x_valid-b_x_valid))} at {torch.argmax(torch.abs(batch_x_valid-b_x_valid))}'

    @pytest.mark.unit
    @pytest.mark.parametrize('fft_length', [128, 1024])
    @pytest.mark.parametrize('num_channels', [1, 4])
    @pytest.mark.parametrize('magnitude_power', [0.5, 1, 2])
    @pytest.mark.parametrize('scale', [0.1, 1.0])
    def test_audio_to_spectrogram_reconstruction(
        self, fft_length: int, num_channels: int, magnitude_power: float, scale: float
    ):
        """Test analysis and synthesis transform result in a perfect reconstruction."""
        batch_size = 4
        num_samples = fft_length * 50
        num_examples = 25
        random_seed = 42
        atol = 1e-6

        _rng = np.random.default_rng(seed=random_seed)

        hop_lengths = [fft_length // 2, fft_length // 4]

        for hop_length in hop_lengths:
            audio2spec = AudioToSpectrogram(
                fft_length=fft_length, hop_length=hop_length, magnitude_power=magnitude_power, scale=scale
            )
            spec2audio = SpectrogramToAudio(
                fft_length=fft_length, hop_length=hop_length, magnitude_power=magnitude_power, scale=scale
            )

            for n in range(num_examples):
                x = _rng.normal(size=(batch_size, num_channels, num_samples))

                x_spec, x_spec_length = audio2spec(input=torch.Tensor(x))
                x_hat, x_hat_length = spec2audio(input=x_spec, input_length=x_spec_length)

                assert np.allclose(
                    x_hat.cpu().detach().numpy(), x, atol=atol
                ), f'Reconstructed not matching for example {n} (hop length {hop_length})'

    @pytest.mark.unit
    @pytest.mark.parametrize('fft_length', [128, 512])
    @pytest.mark.parametrize('num_channels', [1, 4])
    @pytest.mark.parametrize('magnitude_power', [0.5, 1])
    @pytest.mark.parametrize('scale', [0.1, 1.0])
    def test_match_reference_implementation(
        self, fft_length: int, num_channels: int, magnitude_power: float, scale: float
    ):
        """Test analysis and synthesis transforms match reference implementation."""
        batch_size = 4
        num_samples = fft_length * 50
        num_examples = 8
        random_seed = 42
        atol = 1e-6

        _rng = np.random.default_rng(seed=random_seed)

        hop_lengths = [fft_length // 2, fft_length // 4]

        for hop_length in hop_lengths:
            audio2spec = AudioToSpectrogram(
                fft_length=fft_length, hop_length=hop_length, magnitude_power=magnitude_power, scale=scale
            )
            spec2audio = SpectrogramToAudio(
                fft_length=fft_length, hop_length=hop_length, magnitude_power=magnitude_power, scale=scale
            )

            # Reference implementations
            ref_window = torch.hann_window(fft_length)

            def audio2spec_ref(x):
                # Transform each channel and batch example separately
                x_spec = []
                for b in range(batch_size):
                    for c in range(num_channels):
                        x_spec_bc = torch.stft(
                            input=x[b, c, :],
                            n_fft=fft_length,
                            hop_length=hop_length,
                            win_length=fft_length,
                            window=ref_window,
                            center=True,
                            pad_mode='constant',
                            normalized=False,
                            onesided=True,
                            return_complex=True,
                        )
                        x_spec.append(x_spec_bc)
                x_spec = torch.stack(x_spec, dim=0)
                x_spec = rearrange(x_spec, '(B C) F N -> B C F N', B=batch_size, C=num_channels)
                # magnitude compression and scaling
                x_spec = (
                    torch.pow(x_spec.abs(), magnitude_power) * torch.exp(1j * x_spec.angle())
                    if magnitude_power != 1
                    else x_spec
                )
                x_spec = x_spec * scale if scale != 1 else x_spec
                return x_spec

            def spec2audio_ref(x_spec):
                # scaling and magnitude compression
                x_spec = x_spec / scale if scale != 1 else x_spec
                x_spec = (
                    torch.pow(x_spec.abs(), 1 / magnitude_power) * torch.exp(1j * x_spec.angle())
                    if magnitude_power != 1
                    else x_spec
                )
                # Transform each channel and batch example separately
                x = []
                for b in range(batch_size):
                    for c in range(num_channels):
                        x_bc = torch.istft(
                            input=x_spec[b, c, ...],
                            n_fft=fft_length,
                            hop_length=hop_length,
                            win_length=fft_length,
                            window=ref_window,
                            center=True,
                            normalized=False,
                            onesided=True,
                            return_complex=False,
                        )
                        x.append(x_bc)
                x = torch.stack(x, dim=0)
                x = rearrange(x, '(B C) T -> B C T', B=batch_size, C=num_channels)
                return x

            for n in range(num_examples):
                x = _rng.normal(size=(batch_size, num_channels, num_samples))

                # Test analysis
                x_spec, x_spec_length = audio2spec(input=torch.Tensor(x))
                x_spec_ref = audio2spec_ref(torch.Tensor(x))

                assert torch.allclose(
                    x_spec, x_spec_ref, atol=atol
                ), f'Analysis not matching for example {n} (hop length {hop_length})'

                # Test synthesis
                x_hat, _ = spec2audio(input=x_spec, input_length=x_spec_length)
                x_hat_ref = spec2audio_ref(x_spec_ref)

                assert torch.allclose(
                    x_hat, x_hat_ref, atol=atol
                ), f'Synthesis not matching for example {n} (hop length {hop_length})'

    @pytest.mark.unit
    @pytest.mark.parametrize('fft_length', [13, 63])
    def test_invalid_length(self, fft_length: int):
        """Test initializing transforms with invalid length."""

        # Only even fft lengths are supported
        with pytest.raises(ValueError):
            AudioToSpectrogram(fft_length=fft_length, hop_length=fft_length // 2)
        with pytest.raises(ValueError):
            SpectrogramToAudio(fft_length=fft_length, hop_length=fft_length // 2)

    @pytest.mark.unit
    @pytest.mark.parametrize('fft_length', [32])
    def test_invalid_compression(self, fft_length: int):
        """Test initializing transforms with invalid compression."""
        # Compression must be positive
        with pytest.raises(ValueError):
            AudioToSpectrogram(fft_length=fft_length, hop_length=fft_length // 2, magnitude_power=0.0)
        with pytest.raises(ValueError):
            SpectrogramToAudio(fft_length=fft_length, hop_length=fft_length // 2, magnitude_power=0.0)
        with pytest.raises(ValueError):
            AudioToSpectrogram(fft_length=fft_length, hop_length=fft_length // 2, magnitude_power=-1.0)
        with pytest.raises(ValueError):
            SpectrogramToAudio(fft_length=fft_length, hop_length=fft_length // 2, magnitude_power=-1.0)

        # Scaling must be positive
        with pytest.raises(ValueError):
            AudioToSpectrogram(fft_length=fft_length, hop_length=fft_length // 2, scale=0.0)
        with pytest.raises(ValueError):
            SpectrogramToAudio(fft_length=fft_length, hop_length=fft_length // 2, scale=0.0)
        with pytest.raises(ValueError):
            AudioToSpectrogram(fft_length=fft_length, hop_length=fft_length // 2, scale=-1.0)
        with pytest.raises(ValueError):
            SpectrogramToAudio(fft_length=fft_length, hop_length=fft_length // 2, scale=-1.0)

    @pytest.mark.unit
    @pytest.mark.parametrize('fft_length', [32])
    def test_invalid_spec_to_audio_input(self, fft_length: int):
        """Test invalid input for spec to audio transform."""
        s2a = SpectrogramToAudio(fft_length=fft_length, hop_length=fft_length // 2)
        # Input must be complex
        s2a(input=torch.randn(1, 1, fft_length // 2 + 1, 100, dtype=torch.cfloat))

        # Input must be complex
        with pytest.raises(ValueError):
            s2a(input=torch.randn(1, 1, fft_length // 2 + 1, 100))

    @pytest.mark.unit
    @pytest.mark.parametrize('fft_length', [256, 512])
    @pytest.mark.parametrize('hop_div', [2, 4])
    @pytest.mark.parametrize('batch_size', [1, 2])
    @pytest.mark.parametrize('num_channels', [1, 2])
    @pytest.mark.parametrize('magnitude_power', [0.5, 1, 2])
    @pytest.mark.parametrize('scale', [0.1, 1.0])
    @pytest.mark.parametrize('chunk_size', [1, 2, 5])
    @pytest.mark.parametrize('window_type', ['rectangular', 'hamming'])
    def test_streaming_istft_matches_offline_rectangular_center_false(
        self,
        fft_length: int,
        hop_div: int,
        batch_size: int,
        num_channels: int,
        magnitude_power: float,
        scale: float,
        chunk_size: int,
        window_type: str,
    ):
        """Streaming iSTFT (frame-by-frame) matches offline torch.istft when
        using rectangular window and center=False.

        Steps:
        - Generate random audio-like signal (Gaussian) of length T
        - Compute STFT offline with center=False and rectangular window
        - Reconstruct via offline torch.istft
        - Reconstruct via SpectrogramToAudio.stream_update one frame at a time, then stream_finalize
        - Compare both reconstructions
        """
        torch.manual_seed(123)
        hop_length = fft_length // hop_div

        # Generate random signal
        T = fft_length * 20 + 5  # non-multiple of hop to exercise edges
        x = torch.randn(batch_size, num_channels, T)

        # Window selection
        if window_type == 'rectangular':
            window = torch.ones(fft_length)
        elif window_type == 'hamming':
            window = torch.hamming_window(fft_length)
        else:
            raise ValueError(f"Unsupported window_type: {window_type}")

        # STFT with center=False
        audio2spec = AudioToSpectrogram(
            fft_length=fft_length, hop_length=hop_length, magnitude_power=magnitude_power, scale=scale, center=False
        )
        audio2spec.window = window

        spec, _ = audio2spec(input=x)

        N = spec.size(-1)

        # Offline reconstruction using SpectrogramToAudio (same class)
        spec2audio_offline = SpectrogramToAudio(
            fft_length=fft_length, hop_length=hop_length, magnitude_power=magnitude_power, scale=scale, center=False
        )
        spec2audio_offline.window = window
        x_offline, _ = spec2audio_offline(input=spec)

        # Streaming iSTFT via SpectrogramToAudio with parametrized chunk size
        spec2audio = SpectrogramToAudio(
            fft_length=fft_length, hop_length=hop_length, magnitude_power=magnitude_power, scale=scale, center=False
        )
        # Switch window
        spec2audio.use_streaming = True
        spec2audio.window = window
        spec2audio.reset_streaming()

        parts = []
        for t in range(0, N, chunk_size):
            # Feed chunk_size frames at a time: shape (B, C, F, K)
            frames = spec[..., t : min(t + chunk_size, N)]
            out, _ = spec2audio(input=frames)
            parts.append(out)
        tail = spec2audio.stream_finalize()
        x_stream = torch.cat(parts + [tail], dim=-1)

        # Compare offline vs streaming
        assert x_stream.shape == x_offline.shape
        assert torch.allclose(
            x_stream, x_offline, atol=1e-5
        ), f"Streaming iSTFT mismatch (chunk_size={chunk_size}): max abs diff {torch.max(torch.abs(x_stream - x_offline))}"