docstr: Test conversions to and from dB.
          
docstr_tok: ["Test","conversions","to","and","from","dB","."]
code: def test_db_conversion(self):
      """Test conversions to and from dB."""
      num_examples = 10
      abs_threshold = 1e-6
  
      mag = np.random.rand(num_examples)
      mag_db = mag2db(mag)
  
      assert all(np.abs(mag - 10 ** (mag_db / 20)) < abs_threshold)
      assert all(
          np.abs(db2mag(mag_db) - 10 ** (mag_db / 20)) < abs_threshold
      )
      assert all(np.abs(pow2db(mag**2) - mag_db) < abs_threshold)
  
imports: import os
  from collections import namedtuple
  from typing import List, Type, Union
  import librosa
  import matplotlib.pyplot
  import numpy
  import pytest
  import scipy
  import soundfile
  import torch
  from nemo.collections.asr.parts.preprocessing.segment import AudioSegment
  from nemo.collections.asr.parts.utils.audio_utils import SOUND_VELOCITY
  from nemo.collections.asr.parts.utils.audio_utils import calculate_sdr_numpy, convmtx_mc_numpy, db2mag, estimated_coherence, generate_approximate_noise_field, get_segment_start, mag2db, pow2db, rms, select_channels, theoretical_coherence, toeplitz
label_desc: Use image node_id 2 for calling the TestAudioUtilsElements obj's underlying member method code with example usage: obj.test_db_conversion() without return types