AMR HR frame lengths are different. AMR utilizes discontinuous transmission (DTX), with voice activity detection (VAD) and comfort noise generation (CNG) to reduce bandwidth usage during silence periods Algorithmic delay is 20 ms per frame. For bit-rates of 12.2, there is no "algorithm" look-ahead delay. For other rates, look-ahead delay is 5 ms. Note that there is 5 ms "dummy" look-ahead delay, to allow seamless frame-wise mode switching with the rest of rates. AMR is a hybrid speech coder, and as such transmits both speech parameters and a waveform signal Linear predictive coding (LPC) is used to synthesize the speech from a residual waveform. The LPC parameters are encoded as line spectral pairs (LSP). The residual waveform is coded using algebraic code-excited linear prediction (ACELP). The complexity of the algorithm is rated at 5, using a relative scale where G.711 is 1 and G.729a is 15. PSQM testing under ideal conditions yields mean opinion scores of 4.14 for AMR (12.2 kbit/s), compared to 4.45 for G.711 (μ-law) PSQM testing under network stress yields mean opinion scores of 3.79 for AMR (12.2 kbit/s), compared to 4.13 for G.711 (μ-law) Licensing and patent issues AMR codecs incorporate several patents of Nokia, Ericsson, NTT and VoiceAge, the last one being the License Administrator for the AMR patent pools. VoiceAge also accepts submission of patents for determination of their possible essentiality to these standards. However, it's very difficult to determine if there were actually any patents in existence for the so-called inventions related to AMR/AMR-WB codecs, since inventors (and their lawyers) do everything they can to hide patents related to AMR/AMR-WB technology. Apparently, all these patents are hidden from all other researches and general audience that could perhaps spot prior art in the claimed "inventions" patented by the patent holders of the AMR/AMR-WB codecs. The initial fee for professional content creation tools and "real-time channel" products is US$6,500. The minimum annual royalty is $10,000, which, in the first year, excludes the initial fee. Per-channel license fees fall from $0.99 to $0.50 with volume, up to a maximum of $2 million annually. In the category of personal computer products, e.g., media players, the AMR decoder is licensed for free. The license fee for a sold encoder falls from $0.40 to $0.30 with volume, up to a maximum of $300,000 annually. The minimum annual royalty is not applied to licensed products that fall under the category