What is an .amr file? _.amr file science

Many of you may not know what .amr file is now, but in the semi-smartphone era of Nokia, .amr format files abounded. The .amr file is a speech encoding file, and most of the ringtones and recordings used in Nokia's semi-smartphone era were in .amr format, which is more professionally described as: sampling rate 8 kHz/13-bit (160 samples per 20ms), and only the signal in the 200-3400 Hz range is retained after filtering.

Of course, with the advancement of technology and the iteration of smartphones, there are still fewer .amr files in use, and only the voices in software such as QQ and WeChat are still in this format. Because the .amr format does not have any optimization compression on the voice, it can retain the most realistic degree of voice!

Features

• Sampling rate 8 kHz/13-bit (160 sampling points every 20 ms), filtered to retain only signals in the 200-3400 Hz range.
• The encoder uses 8 bit rates: 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbit/s.
• The generated frame lengths are 95, 103, 118, 134, 148, 159, 204, or 244 bits, corresponding to bit speeds of 4.75, 5.15, 5.90, 6.70, 7.40, 7.95, 10.2, or 12.2 kbit/s, respectively.
• AMR uses Discontinuous Transmission (DTX), Voice Activity Detection (VAD) and Comfort
• Noise Generation (CNG) to reduce the bandwidth during silent times.
• The algorithm latency is 20 ms per frame, and at a bit rate of 12.2, there is no look-ahead latency. The look-ahead delay for other rates is 5 ms. Note that a 5 ms faux look-ahead delay allows accurate frame-width pattern conversion for the remaining rates.
• AMR is a hybrid language encoder using Algebraic Code Excited Linear Prediction (ACELP).
  If the complexity of the algorithm is 5, then G.711 is 1 and G.729a is 15.
• PSQM tested under ideal conditions with lossy Mean Opinion Scores AMR (12.2 kbit/s) is 4.14, compared to G.711 (u-law) which is 4.45.
• PSQM under network conditions Mean Opinion Scores AMR (12.2 kbit/s) is 3.79 compared to G.711 (u-law) which is 4.13.