(1) Redundant information of audio signal
If the digital audio signal is transmitted directly without compression, it will occupy a huge bandwidth. For example, if the sampling frequency of a set of dual channel digital audio is 44.1KHz and each sample value is quantized by 16bit, the code rate is:
2*44.1kHz*16bit=1.411Mbit/s
Such a large bandwidth will bring many difficulties to the signal transmission and processing, so we must adopt the audio compression technology to process the audio data, in order to effectively transmit the audio data.
Digital audio compression coding can compress the audio data signal as much as possible on the premise that the signal does not produce distortion in hearing. Digital audio compression coding is realized by removing redundant components in sound signal. The so-called redundant components refer to the signals in the audio that can not be perceived by the human ear. They have no help in determining the timbre, tone and other information of the sound.
Redundant signals include audio signals beyond the range of human hearing and audio signals that are masked. For example, the frequency range of sound signal that can be detected by human ear is 20Hz ~ 20kHz, and other frequencies that cannot be detected by human ear can be regarded as redundant signals. In addition, according to the physiological and psychoacoustic phenomenon of human hearing, when a strong tone signal and a weak tone signal exist at the same time, the weak tone signal will be masked by the strong tone signal and can not be heard, so the weak tone signal can be regarded as redundant signal instead of transmission. This is the masking effect of human hearing, which is mainly manifested in the spectrum masking effect and the time-domain masking effect
(a) Spectrum masking effect
When the sound energy of a frequency is less than a certain threshold, the human ear will not hear it. This threshold is called the minimum audible threshold. When another sound with higher energy appears, the threshold near the sound frequency will increase a lot, which is called masking effect.
From the figure, we can see that the human ear is most sensitive to the sound of 2KHz ~ 5KHz, and is very insensitive to the sound signal with too low or too high frequency. When a sound with frequency of 0.2khz and intensity of 60dB appears, the threshold near it increases a lot. From the figure, we can see that the part below 0.1khz and above 1kHz is far away from the strong signal of 0.2khz, so it is not affected by the strong signal of 0.2khz, and the threshold is not affected; while in the range of 0.1khz-1khz, due to the appearance of strong tone of 0.2khz, the threshold is greatly improved, and the minimum sound intensity that the human ear can feel in this range is greatly improved. If the intensity of the sound signal in the range of 0.1khz ~ 1kHz is below the threshold curve, because it is masked by the 0.2khz strong tone signal, then our ears can only hear the strong tone signal of 0.2khz at this time, but can not hear other weak signals at all. These weak tone signals existing at the same time with the strong tone signal of 0.2khz can be regarded as redundant signals and need not be transmitted.
(b) Time domain masking effect
When strong tone signal and weak tone signal appear at the same time, there is also time-domain masking effect. That is to say, when the occurrence time of the two is very close, the masking effect will also occur. The time-domain masking process curve is shown in the figure, which is divided into three parts: front masking, simultaneous masking and back masking.
The time-domain masking effect can be divided into three types: front masking, simultaneous masking and back masking. Pre masking means that the existing weak signal will be masked and not be heard in a short time before the human ear hears the strong signal. Simultaneous masking means that when the strong signal and the weak signal exist at the same time, the weak signal will be masked by the strong signal and not be heard. Post masking refers to that when the strong signal disappears, it takes a long time to hear the weak signal again, which is called post masking. These signals can be regarded as redundant signals.
(c) Compression coding method
At present, there are different coding schemes and implementation methods in the field of digital audio coding, but the basic coding ideas are similar, as shown in the figure.
For each audio channel, it is necessary to map them to the frequency domain, which can be realized by subband filter. The audio sampling block in each channel first calculates the masking threshold value according to the psychoacoustic model, and then determines the number of bits in different frequency domains allocated to the channel from the common bit pool according to the calculated masking threshold value, and then carries out quantization and coding, and finally adds the control parameters and auxiliary data into the data to generate the encoded data stream.
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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.
Our solution has FM Radio Station / Analog TV Station / Digital TV Station / Audio Video Studio Equipment / Studio Transmitter Link / Transmitter Telemetry System / Hotel TV System / IPTV Live Broadcasting / Streaming Live Broadcast / Video Conference / CATV Broadcasting system.
We are using advanced technology products for all the systems, because we know the high reliability and high performance are so important for the system and solution . At the same time we also have to make sure our products system with a very reasonable price.
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 .
FMUSER.ORG has been exporting more than 15 years and have clients all over the world. With 13 years experience in this field ,we have a professional team to solve customer's all kinds of problems. We dedicated in supplying the extremely reasonable pricing of professional products & services. Contact email : [email protected]
Our Factory
We have modernization of the factory . You are welcome to visit our factory when you come to China.
At present , there are already 1095 customers around the world visited our Guangzhou Tianhe office . If you come to China , you are welcome to visit us .
At Fair
This is our participation in 2012 Global Sources Hong Kong Electronics Fair . Customers from all over the world finally have a chance to get together.
Where is Fmuser ?
You can search this numbers " 23.127460034623816,113.33224654197693 " in google map , then you can find our fmuser office .
FMUSER Guangzhou office is in Tianhe District which is the center of the Canton . Very near to the Canton Fair , guangzhou railway station, xiaobei road and dashatou , only need 10 minutes if take TAXI . Welcome friends around the world to visit and negotiate .
Contact: Sky Blue
Cellphone: +8618078869184
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E-mail: [email protected]
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Skype: sky198710021
Address: No.305 Room HuiLan Building No.273 Huanpu Road Guangzhou China Zip:510620
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English: We accept all payments , such as PayPal, Credit Card, Western Union, Alipay, Money Bookers, T/T, LC, DP, DA, OA, Payoneer, If you have any question , please contact me [email protected] or WhatsApp +8618078869184
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First BANK INFORMATION (COMPANY ACCOUNT):
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Account Name : FMUSER INTERNATIONAL GROUP LIMITED
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Second BANK INFORMATION (COMPANY ACCOUNT):
Beneficiary: Fmuser International Group Inc
Account Number: 44050158090900000337
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* It will be sent in 1-2 working days when payment clear.
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* If the packages is below 2kg,we will be shipped via post airmail, it will take about 15-25days to your hand.
If the package is more than 2kg,we will ship via EMS , DHL , UPS, Fedex fast express delivery,it will take about 7~15days to your hand.
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For Warranty .
Contact US--->>Return the item to us--->>Receive and send another replace .
Name: Liu xiaoxia
Address: 305Fang HuiLanGe HuangPuDaDaoXi 273Hao TianHeQu Guangzhou China.
ZIP:510620
Phone: +8618078869184
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