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I decode an mp3 song using two different methods. The output PCM signals are shown in Figure 1 and Figure 2 respectively. Both the decoded output files have the same file size and audio quality. However, there exist some difference between the PCM signals. What causes the spike in PCM signal?

Figure

1

These spikes are high frequency components contained in the resulting signal decode. There are two possible reasons for this.

  1. Method one uses a low pass filter which removes these components.
  2. Method two has a decoding fault.

Both of these suggestions are speculative as there is no reference signal to compare.

  • There's obviously a difference between the implementations. If the algorithm is the same then your assumption is correct - the result should be the same, but it's evident that the results are different, therefore the answer will be an issue with the implemenations of the algorithm. More than that, I can't say without examples. You would possibly find some more assistance on dsp.stackexchange.com – Mark Dec 28 '19 at 6:44

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