The full name is Adaptive Multi-Rate, adaptive multi-rate encoding, mainly used for audio in mobile devices. The compression ratio is relatively large, but the quality is relatively poor compared to other compression formats. Because it is mostly used for human voice and calls, the effect is still very good.
1. Classification
1) AMR: Also known as AMR-NB, relative to the following WB, Voice bandwidth range: 300-3400Hz, 8KHz sampling
2) AMR-WB: AMR WideBand, Voice bandwidth range: 50-7000Hz 16KHz sampling.
The full name of "AMR-WB" is "Adaptive Multi-rate-Wideband", that is, "Adaptive Multi-rate Wideband Coding". The sampling frequency is 16kHz. It is a wideband speech coding standard adopted by the International Organization for Standardization ITU-T and 3GPP. , Also known as the G722.2 standard. AMR-WB provides a voice bandwidth range of 50～7000Hz, and users can subjectively feel that the voice is more natural, comfortable and easy to distinguish than before. Compared with this, the current EFR (Enhenced Full Rate, enhanced full rate coding) sampling frequency used by GSM is 8kHz, and the speech bandwidth is 200～3400Hz. The advantage of AMR-WB applied to narrow-band GSM (full-speed channel 16k, GMSK) is that it can use three encodings from 6.6kb/s, 8.85kb/s and 12.65kb/s. When the network is busy, C/I deteriorates, the encoder The encoding mode can be automatically adjusted to enhance QoS. In this application, AMR-WB has better noise immunity than AMR-NB. The application of AMR-WB to EDGE and 3G can fully reflect its advantages. Adequate transmission bandwidth guarantees that AMR-WB can use a total of nine encodings ranging from 6.6kb/s to 23.85kb/s, and the voice quality exceeds that of PSTN fixed telephones.
2. coding method
1) AMR-NB: AMR has a total of 16 encoding methods, 0-7 corresponds to 8 different encoding methods, and 8-15 is used for noise or reserved.
2) AMR-WB:
2. AMR frame format
AMR has two types of frame formats: AMR IF1 and AMR IF2 1.
The data of each frame is divided into three parts: Class A/B/C
Class A: The most sensitive and important data in a frame. Once this part of the data is damaged, the entire frame cannot be decoded and is damaged. Therefore, various redundant methods are generally used to protect this part of the data during wireless transmission.
Class B: Data that is less important than Class A.
Class C: Data that is less important than Class B.
2. AMR IF2
Compared with IF1, IF2 saves Frame Quality Indicator, Mode Indication, Mode Request and CRC check. However, bit padding is added. Because the length of the data in the AMR frame is not an integer multiple of bytes (8 bits), bit padding needs to be added at the end of some frames to make the length of the entire frame reach an integer multiple of bytes.
3. frame size
1) AMR-NB
Number of bits in Classes A, B, and C for each AMR codec mode
4. the conversion between PCM16 and AMR Amr
one frame is 20 milliseconds Take AMR 4.75Kbits/s as an example: The number of sound bits produced per second = 4750bits/s The number of bits occupied per 20ms frame = 4750bits/s / 50frames/s = 95bits The number of bytes occupied per 20ms frame = 95bits / 8bits/byte = 11.875bytes-rounded to 12 bytes, and 0 is missing Add a byte of the frame header, so the AMR of a frame of 20ms: 12-bytes + 1-byte = 13-bytes Instead, switch back to become 13-bytes * 50frames/s * 8bits/byte = 5200bits/s Note that the two values here do not correspond, it is due to rounding 5. The storage format of AMR files (RFC 3267): AMR IF1, IF2 define the frame format of AMR, which is used for wireless transmission. RFC 3267 defines the file format for saving AMR data as a file. The file format of AMR is shown in Figure 1 below: It contains a file header and then AMR data frame by frame.1. File header format: AMR files support mono and multi-channel. The file headers of mono and multi-channel are different. Mono: AMR-NB file header: "#!AMR"n" (or 0x2321414d520a in hexadecimal) (the part in quotation marks) AMR-WB file header: "#!AMR-WB"n" (or 0x2321414d522d57420a in hexadecimal). (in quotation marks) Multi-channel: The multi-channel file header contains a magic number and 32bit channle description fields. The magic number of AMR-NB: "#!AMR_MC1.0"n" (or 0x2321414d525F4D43312E300a in hexadecimal). The magic number of AMR-WB: "#!AMR-WB_MC1.0"n" (or 0x2321414d522d57425F4D43312E300a in hexadecimal). The 32bit channel description field is defined as follows: The reserved bits must be 0, and CHAN: indicates that the current file contains several channels. The format of the frame header: The format of the frame header is shown in Figure 2. It occupies 1 byte (8 bits) P is filled to be set to 0 FT is the coding mode, that is, the 16 coding modes mentioned above. Q is the frame quality indicator. If it is 0, the frame is damaged. Figure 3 lists the format of a frame of AMR-NB 5.9Kbit, For a 5.9kbit frame with 118bit data, 15*8=120=118+2, so there are 2 bits of padding at the end. references: RFC3267 RTP Payload Format for AMR and AMR-WB 3GPP TS 26.201 V6.0.0 3GPP TS 26.101 V6.0.0
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How far(long) the transmitter cover?
The transmission range depends on many factors. The true distance is based on the antenna installing height , antenna gain, using environment like building and other obstructions , sensitivity of the receiver, antenna of the receiver . Installing antenna more high and using in the countryside , the distance will much more far.
EXAMPLE 5W FM Transmitter use in the city and hometown:
I have a USA customer use 5W fm transmitter with GP antenna in his hometown ,and he test it with a car, it cover 10km(6.21mile).
I test the 5W fm transmitter with GP antenna in my hometown ,it cover about 2km(1.24mile).
I test the 5W fm transmitter with GP antenna in Guangzhou city ,it cover about only 300meter(984ft).
Below are the approximate range of different power FM Transmitters. ( The range is diameter )
0.1W ~ 5W FM Transmitter ：100M ~1KM
5W ~15W FM Ttransmitter : 1KM ~ 3KM
15W ~ 80W FM Transmitter : 3KM ~10KM
80W ~500W FM Transmitter : 10KM ~30KM
500W ~1000W FM Transmitter : 30KM ~ 50KM
1KW ~ 2KW FM Transmitter : 50KM ~100KM
2KW ~5KW FM Transmitter : 100KM ~150KM
5KW ~10KW FM Transmitter : 150KM ~200KM
How to contact us for the transmitter?
Call me +8618078869184 OR
Email me [email protected]
1.How far you want to cover in diameter ?
2.How tall of you tower ?
3.Where are you from ?
And we will give you more professional advice.
About Us
FMUSER.ORG is a system integration company focusing on RF wireless transmission / studio video audio equipment / streaming and data processing .We are providing everything from advice and consultancy through rack integration to installation, commissioning and training.
We offer FM Transmitter, Analog TV Transmitter, Digital TV transmitter, VHF UHF Transmitter, Antennas, Coaxial Cable Connectors, STL, On Air Processing, Broadcast Products for the Studio, RF Signal Monitoring, RDS Encoders, Audio Processors and Remote Site Control Units, IPTV Products, Video / Audio Encoder / Decoder, designed to meet the needs of both large international broadcast networks and small private stations alike.
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We have customers of public and commercial broadcasters, telecom operators and regulation authorities , and we also offer solution and products to many hundreds of smaller, local and community broadcasters .
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