What is the Difference Between PCM and ADPCM?

06/02/2025 • Felipe Moraes

The main difference between Pulse Code Modulation (PCM) and Adaptive Differential Pulse Code Modulation (ADPCM) lies in their encoding methods, compression, and trade-off between audio quality and bandwidth. Here are the key differences:

  1. Encoding Method: PCM is a direct representation of the audio signal using sample values, while ADPCM is a variant of Differential Pulse Code Modulation (DPCM) that sends the difference between consecutive samples instead of the entire sample values.
  2. Compression: PCM is a lossless encoding method that provides the highest accuracy but requires the most bandwidth. ADPCM is a lossy encoding method that sacrifices some accuracy to achieve better compression and reduce the required bandwidth.
  3. Audio Quality: PCM is ideal for situations where high-quality audio is required, while ADPCM is suitable for scenarios where the duration of the audio file is more important than the audio quality.
  4. Bandwidth: PCM needs a fixed and larger number of bits to represent a signal, while ADPCM requires a smaller number of bits due to its adaptive quantization step and prediction coding.
  5. Decoding: Decoding a PCM signal is easier than decoding an ADPCM signal, as PCM directly uses sample values, while ADPCM uses prediction and a predefined index of sample values.

In summary, PCM is preferred for high-quality audio when bandwidth is not a constraint, while ADPCM is used for scenarios where bandwidth is limited, and some loss of audio quality can be tolerated.

Comparative Table: PCM vs ADPCM

Here is a table comparing the differences between PCM (Pulse Code Modulation) and ADPCM (Adaptive Differential Pulse Code Modulation):

Feature PCM ADPCM
Definition PCM is a technique used to convert analog signals into digital signals. ADPCM is a variant of Differential Pulse Code Modulation (DPCM) that adjusts the step size of the quantization based on the signal.
Representation Sample values are directly used to represent the signal. The difference between two consecutive samples is used to represent the signal.
Sampling Interval The size of the interval between two samples is fixed. The size of the interval between two samples can be varied.
Compression PCM requires a higher number of bits to represent a signal compared to ADPCM. ADPCM needs a lesser number of bits to represent a signal compared to PCM.
Decoding Decoding a PCM signal is easier than decoding an ADPCM signal. ADPCM is widely used in many encoding applications due to its efficient use of bits.

In summary, PCM is a technique that directly represents analog signals with digital samples, while ADPCM is a more efficient variant of DPCM that encodes the differences between consecutive samples instead of the entire sample values. ADPCM is widely used in various encoding applications due to its ability to reduce the number of bits needed to represent a signal.

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