WO2009050721A2

WO2009050721A2 - Method and system for processing audio in a telecommunication network

Info

Publication number: WO2009050721A2
Application number: PCT/IN2007/000607
Authority: WO
Inventors: Madhavan Brijith Viyayavihar
Original assignee: Onmobile Global Limited
Priority date: 2007-10-16
Filing date: 2007-12-27
Publication date: 2009-04-23
Also published as: WO2009050721A3

Abstract

A method and a system for processing audio in a telecommunication system are disclosed. The sampling rate of the audio file is reduced to a pre-specified sampling rate. Thereafter, the frequency of the audio file is adjusted using certain parameters. Then, the amplitude of the audio file is modified so that the average peak amplitude is close to a desired amplitude value. This is followed by hard limiting of the audio file to ensure that peak amplitude never crosses a certain pre-specified value. The processed audio file is then transmitted over the telecommunication network.

Description

-I ITLEΪ "METHOD AND SYSTEM FOR PROCESSING AUDIO IN A

TELECOMMUNICATION NETWORK" FIELD OF THE INVENTION

The present invention relates to processing of audio signal in a telecommunication system. More specifically, the invention relates to processing of a ring back tone for improving the audio quality of the ring back tone in a telecommunication system.

DEFINITIONS

Caller: The mobile phone user who initiates a call is called a 'caller'

Callee: The mobile phone user to whom the call is made is called a 'callee'

Ring back Tone (RBT): A tone which is played to the caller while he/she is waiting for the callee to respond to the call is called an RBT. The RBT is played till the callee responds to the call.

BACKGROUND OF INVENTION

Telecommunication service providers provide services enabling an individual to communicate with other individuals using telecommunication terminals like a fixed landline telephone, cellular phone etc. The number of mobile phone users has increased considerably during recent times. With the increase in number of mobile phone users, there has been an increase in the number of value added services that are offered to the mobile phone users. Stiff competition has compelled the providers of the value added services to provide innovative services and improve upon the existing services that are provided to the mobile phone users. Ring Back Tone (RBT) service is one such example of value added services provided to the mobile phone users.

When a calling party, hereinafter referred to as a caller, makes a call to a called party, hereinafter referred to as a callee, using a telecommunication terminal, the caller hears a call progress tone. A call progress tone is an intermittent tone heard by the caller after dialing and prior to the call being answered by the callee at the receiving end. The call progress tone may be a ring-back tone (RBT), busy tone, call-waiting tone or a combination thereof. An RBT is conventionally a monotonous tone heard by a calling party while waiting for a called party to respond to the call. me _KB i , conven ona y a mono onous soun , can e epiaceα oy oin tones, for example, songs, music, news recordings, sports commentary etc. Such tones are more pleasing, than a monotonous sound, for the caller as the caller waits for the callee to respond to the call. An individual may select an RBT of her own choice, by subscribing to an RBT service generally provided by the telecommunication service provider.

The popularity of the RBT service provided by a particular service provider depends considerably on the audio quality of RBT played. An RBT of superior audio quality is likely to attract more individuals subscribing for the RBT service. An inferior audio quality of RBT might result in a potential customer not subscribing to the RBT service; or an existing RBT subscriber de-subscribing from the RBT service. Therefore, there is a need for a good quality RBT signal.

Various factors adversely affect the audio quality of the RBT. The RBT may have various kinds of noise, such as clicks, clipping, rumble, hiss, hum and a combination thereof. In addition, the RBT quality is also adversely affected by reverberation, and interference with other already existing audio signals. Equalizers provide broad adjustments of various frequency bands like treble, bass, midrange and the likes. However, there is a need to provide independent control over the low bass, mid-bass, high bass, low midrange, and the likes.

Further, the equipments used for a telecommunication connection, including speakers of the phone, codecs and the likes are suited for voice transmission only. These equipments are not suited for sounds, which have a greater range of frequencies. Typically, RBTs comprise songs and other rich sounds that are not clearly transmissible or audible using the current equipments.

Moreover, sometimes prompt, containing information about the audio file being played as RBT, is also played along with the RBT. The prompt audio, when transmitted in the telecommunication system, has similar quality problems like RBT as discussed above. There is a need of a good audio quality for the prompt played. Therefore, there is a nee or a sys em or preprocess ng , e ore e RBT is transmitted to the caller, to improve the audio quality of RBT, thus making the RBT mellifluous to an RBT listener in a telecommunication system. There is also a need for preprocessing the prompt played along with the RBT for improving the audio quality of the prompt.

SUMMARY OF THE INVENTION

A method and a system for processing Ring Back Tone (RBT) in a telecommunication system are disclosed. The method comprises processing the RBT audio file before transmitting the file to the caller in a telecommunication network. The RBT audio file is imported into a RBT audio file processor in a prescribed format. Thereafter, the sampling rate of the RBT audio file is reduced to a pre-specified sampling rate. Further, the frequency of the RBT audio file is adjusted. Then, the peak amplitude of the RBT audio file is modified so that the peak amplitude is close to desired amplitude. This is followed by hard limiting of the RBT audio file to ensure that peak amplitude never crosses a certain pre- specified value.

The method further comprises processing a RBT notification audio file in a manner similar to the processing of RBT audio file. The RBT audio file and the RBT notification audio file are then integrated to generate a hybrid RBT audio file. The hybrid RBT audio file is then transmitted through the telecommunication network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a telecommunication infrastructure in accordance with an embodiment of the invention.

FIG. 2 is a schematic illustrating a system for processing RBT audio file, in accordance with an embodiment of the invention.

FIG. 3 is a flowchart depicting a method for processing an RBT audio file, in accordance with an embodiment of the invention.

FIG. 4 is a schematic illustrating the components of the system for processing RBT audio file, in accordance with an embodiment of the invention.

FIG. 5A, FIG. 5B, FIG. 5C are a detail flowchart illustrating the steps of the method for processing an RBT audio file, in accordance with an embodiment of the invention. FIG. 6 is a flowchart illustrating a method for generating a hybrid RBT au o file, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF INVENTION

In the following description, specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent that the invention may be practiced without these specific details. Various aspects and features of example embodiments of the invention are described in more detail hereinafter. A method and a system for processing Ring Back Tone (RBT) in a telecommunication network are disclosed.

FIG. 1 illustrates a telecommunication infrastructure in accordance with an embodiment of the invention. A caller 102 is connected to a telecommunication infrastructure 100 for making a call to a callee 104. Caller 102 and callee 104 may use a telecommunication terminal like a fixed landline telephone, mobile telephone, and the likes, hereinafter referred to as mobile phone, to connect to telecommunication infrastructure 100. Telecommunication infrastructure 100 comprises switching centers for e.g. a Mobile Switching Center (MSC) 106 for enabling a call connection between caller 102 and callee 104.

Telecommunication infrastructure 100 also comprises an information storage module used to store subscription information related to subscribers of the telecommunication service. An example of the information storage module is a Home Location Register (HLR) 108. For each subscriber, the subscription information comprises a unique identifier for the subscriber, telephone number of the subscriber, current location of the subscriber, various services the subscriber has registered for and the likes.

In this scenario, when caller 102 initiates a call with callee 104 using a mobile phone, the call is forwarded to MSC 106. MSC 106 establishes a call connection with callee 104. After a call connection is established with callee 104, i.e. the mobile phone of callee 104 starts ringing; a switch at MSC 106 forwards the call to RBT module 110. RBT module 1 10 is responsible for playing an RBT audio file, which caller 102 hears as an RBT. FIG. 2 is a schematic illustrating a system for processing RBT audio file, in accordance with an embodiment of the invention. As discussed in the background, processing of the RBT audio file is done to improve the audio quality of RBT played to 'caller 102.

An RBT audio file, in a prescribed format, is processed using an RBT audio file processor 200. RBT audio file processor 200 may be in form of software, hardware or a combination thereof. An example of RBT audio file processor 200 in software form is Adobe Audition™, which is a publicly available software application.

RBT audio file processor 200 converts audio files from a particular format and parameters into another format and specifications. Formats of the audio files may be, for example, MP3, WAV, CDDA, OGG, AAC and the likes. Typically, songs sold in a compact disc are in WAV or CDDA format. Parameters for conversion of an audio file may include, for example, sample size, sample rate, channel, bit rate and the likes.

Sample rate defines the number of samples per second (or per other unit) taken from a continuous audio signal to make a discrete audio signal. Sample size denotes the size of each chosen sample of the audio signal in terms of bits. Channels are the number of different audio signals that are played simultaneously. Bit rate is the amount of audio information per second or other time period present in the audio signal.

The format of the file is typically WAV or CDDA as the unprocessed RBTs are taken directly from an audio CD. Following are the typical parameters for the RBT audio file to be processed: Sample rate - 44.1 KHz, Sample Size - 16 bit, Channel - Stereo, and Bit Rate - 1411 kbps

In case the RBT audio file is in MP3/ WMA format, following are the prescribed parameters: Sample rate - 44.1 KHz, Sample Size - 16 bit, Channel - Stereo, and Bit Rate - 128 kbps

WAV/CDDA format is generally preferred to MP3/WMA format because in MP3/WMA format there is more loss of data during compression in MP3/WMA format than in WAV/CDDA format. Also, MP3/WMA requires manual check to ensure audio quality.

RBT audio file processor 200 comprises an RBT audio file down sampler 202, an RBT audio file frequency adjuster 204, and an RBT audio file dynamic processor 206. RBT audio file dynamic processor 206 further comprises an RBT audio file amplitude modifier 208, and an RBT audio file hard limiter 210. RBT audio file down sampler 202 is used for altering the parameters of the RBT audio file. For example, RBT audio file down sampler 202 reduces the sampling rate of an audio file to a prescribed sampling rate. Further, RBT audio file down sampler 202 can also alter the bit rate, sampling size and channel of the audio file. RBT audio file down sampler 202 may for example be a software application running on a computer. RBT audio file frequency adjuster 204 is used for adjusting frequency levels of the RBT audio file. RBT audio file frequency adjuster may be a graphic equalizer, or a high pass filter, in hardware or software form. RBT audio file amplitude modifier 208 is used for increasing or reducing the amplitude of the RBT audio file. RBT audio file hard limiter 210 is used for ensuring that the maximum amplitude value of the RBT audio file is below a prescribed amplitude value. RBT audio file hard limiter 210 is responsible for eliminating noise above and below a particular amplitude value of the RBT audio file.

The method for processing the RBT audio file using the RBT audio file processor 112 is discussed in conjunction with FIG. 3.

The procedure for processing the RBT audio file is different for GSM and CDMA telecommunication network. FIG. 3 is a flowchart depicting a method for processing an RBT audio file, in accordance with an embodiment of the invention. At step 302, an RBT audio file is received and down-sampled. Down-sampling of RBT audio file includes: reducing the sampling rate of the RBT audio file to a prescribed sampling rate, reducing the number of channels of the RBT audio file, reducing the bit rate of the RBT audio file and likes. It will be apparent to a person skilled in the art that down-sampling of an audio file may include other steps, without deviating from the scope of the invention.

At step 304, RBT audio file frequency adjuster 204 adjusts the frequency of RBT audio file. RBT audio file frequency adjuster 204 reduces the amplitude of bass frequency waveform depending on the intensity of the bass frequency waveform. According to an embodiment of the invention, waveforms of frequency below 200 Hz are regarded as bass frequency waveforms. Steps 302 and 304 are same for GSM and CDMA network.

At step 306, an average peak amplitude value of the RBT audio file is identified. The step identifying average peak may be manual or automated. The average peak amplitude may not be equal to the absolute peak amplitude to the RBT audio file. The amplitude of the RBT audio file is then modified such that the identified average peak amplitude of the RBT audio file is equal to a desired amplitude value. The desired amplitude is different for GSM and CDMA network.

At step 308, certain hard limiting parameters are received. These hard-limiting parameters are then applied to the RBT audio file. The hard-limiting parameters include a specific amplitude value, and all amplitude peaks over that specific amplitude value are chopped, without altering the amplitude values below the specified amplitude value. The steps of the method of FIG. 3 are further discussed in detail in conjunction with FIG. 5.

Although particulars of processing procedures for transmission of audio over GSM and CDMA network has been discussed, it will be apparent to a person skilled in the art that similar particulars may be used for transmission of audio over other networks like, but not limited to, WLL and landline. FIG. 4 is a schematic illustrating the components of the system for processing RBT audio file, in accordance with an embodiment of the invention. RBT audio file processor 200 comprises RBT audio file down sampler 202, RBT audio file frequency adjuster 204, and RBT audio file dynamic processor 206. RBT audio file down sampler 202 further comprises a down-sampling parameters receiver 402. Down-sampling parameters receiver 402 receives parameters for down sampling such as sampling rate, resolution, number of channels, quality, and status of pre/post filter.

RBT audio file frequency adjuster 204 further comprises a frequency filter 404 and a frequency parameters receiver 406. Frequency filter 404 receives amplitude gain parameter for reducing the amplitude of bass frequency waveform depending on the intensity of the bass frequency waveform. Frequency parameters receiver 406 receives parameters for adjusting frequency such as master amplitude gain, accuracy in frequency alterations and amplitude range.

RBT audio file dynamic processor 206 comprises RBT audio file amplitude modifier 208, and RBT audio file hard limiter 210 for applying dynamic compression.

RBT audio file amplitude modifier 208 further comprises an amplitude amplifier 408 and an amplitude reducer 410. Amplitude amplifier 408 increases the amplitude of RBT audio file such that the identified average peak of the RBT audio file has a desired amplitude value. The desired amplitude is discussed in conjunction with FIG. 5C.

RBT audio file hard limiter 210 further comprises a hard limit parameters receiver 412 and a wave smoother 414. Hard limit parameters receiver 412 receives parameters for applying hard limit such as maximum amplitude at which hard limit is to be applied. Wave smoother 414 receives parameters for smoothing the chopped waveform at the beginning and at the end. These parameters include look ahead time and release time. FIG. 5A, FIG. 5B, FIG. 5C are a detail flowchart illustrating the steps of the method for processing an RBT audio file, in accordance with an embodiment of the invention.

At step 502, the RBT audio file is received in the prescribed format described earlier. At step 504, a portion of the RBT audio file is looped such that the portion of the RBT audio file is repeated after every loop. The duration of each loop may be within 25 to 40 seconds. The looping may be achieved by fading out and fading in the portion of the RBT audio file.

At step 506 down-sampling parameter are received. The down sampling parameters, for example, may include: sample rate, resolution, channels and the likes. Following are the typical values of down-sampling parameters that are used for down-sampling RBT audio file: Sample rate: 8 kHz Resolution: 16 bit Channels: mono

Thereafter at step 508, the RBT audio file is down sampled to achieve the down-sampling parameters. Down-sampling can be achieved by several hardware and software tools available in the market. For example, Adobe Audition™ may be used to achieve down-sampling.

At step 510, the intensity of bass frequency of the RBT audio file is checked. Bass frequency is a range of low frequency of an audio file. According to an embodiment of the invention, waveforms of frequency below 200 Hz are regarded as bass frequency waveforms. The intensity of base frequency can be checked manually; by listening to the RBT audio file, or automatically, using software or hardware tools. At step 512, the amplitude of the bass frequency is reduced such that the intensity of the bass frequency is below a prescribed limit. Typically when the amplitude range for software or hardware tool is 180 db, the bass frequency of the RBT audio file is set between 0 db - 90 db. It will be apparent to a person skilled in the art that different tools may have different amplitude ranges and therefore the bass frequency amplitude may be modified appropriately. At step 516, various requency a justing parameiers τor adjusting tne frequency of the RBT audio file are received. Typically, frequency adjusting parameters include amplitude range, and its value is around 4 db to 180 db

Thereafter at step 518, the frequency adjusting parameters are used to process the RBT audio file and produce a processed RBT audio file. Steps 502-518 are same for both GSM and CDMA.

At step 520, an average peak amplitude value of the RBT audio file is identified. The step identifying average peak may be manual or automated. The average peak amplitude may not be equal to the absolute peak amplitude to the RBT audio file. The amplitude of the RBT audio file is then modified such that the identified average peak amplitude of the identified the RBT audio file is equal to a desired amplitude value. The desired amplitude is different for GSM and CDMA network.

The desired average peak amplitude value, in case the RBT audio file is transmitted in GSM network, is -6 db. In case the RBT audio file is to be transmitted in a CDMA network, the desired amplitude is -8 db. In case the average peak amplitude is less than the desired amplitude, at step 522, the amplitude of RBT audio file is increased such that the identified average peak of the RBT audio file is equal to the desired amplitude. In case the peak amplitude is greater than the desired amplitude, at step 524, the amplitude of the RBT audio file is reduced such that the identified average peak of the RBT audio file is equal to the desired amplitude.

In case the RBT audio file is to be transmitted in a GSM network, the hard limit parameter, "maximum amplitude' is set at -8 db. In case of CDMA transmission, the maximum amplitude is set at -10 db.

At step 528, wave smoothening parameters are received. Typically, following are parameters and their values for the smoothing of the chopped waveform: Look ahead time: 10 ms Release time: 100 ms After the application of hard im ting an wave smoo ng, e processe audio file is saved as mu-Law.wav in case of GSM network. In case of CDMA network, at step 532, the processed RBT audio file is saved as A-law.wav. The saving formats as described are used for audio transmission in telecommunication network.

A-law and mu-law are codecs which can compress a 16-bit linear sample down to an 8-bit sample. Codec is hardware or software that compresses and decompresses digital audio signal in a telecommunication network. A-law and mu- law are standard codecs widely available for telecommunication purposes. 1 1 will be apparent to a person skilled in the art that any new or existing codec may be used to accomplish this step without deviating from the scope of the invention.

Typically, the final specification of the processed RBT audio file for telecommunication network using GSM or CDMA technology are as follows: Bit rate - 64 kbps RBT audio sample size - 8bit Channels - 1(mono) RBT audio sample rate - 8 KHz RBT audio format - mu-Law (GSM) /A-Law (CDMA)

Apart from processing audio files, the method of FIGs. 5A, 5B and 5C may be used to process streaming audio in a continuous manner. The streaming audio may be for example a radio station or live sports commentary. In case of streaming audio, the steps of the method of FIGs. 5A, 5B and 5C are executed in real-time manner to continuously process the audio.

According to an embodiment of the invention, a notification audio file, giving information about the RBT audio file, is integrated with the RBT audio file to generate a hybrid RBT audio file. The hybrid RBT audio file is subsequently played to the caller 102. The generation of the hybrid RBT audio file is discussed in detail in FIG. 6. The notification audio file is processed to have the same audio quality as that of the RBT audio file. RBT audio file processor 200 can be used to process the notification audio file along with the RBT audio file.

According to an embodiment of invention, the RBT notification audio file is recorded at the following specifications: Sample rate: 44.1 kHz Resolution: 16bit Channel: mono

An example of a software tool for recording the RBT notification audio file in the prescribed format is Protools™.

The RBT notification audio file after being recorded in the prescribed format is processed using a combination of one or more steps of the method of FIGs. 5A, 5B₁ and 5C. In addition, the processing of the RBT notification audio file further comprises the step of cleaning the RBT notification audio file. Cleaning the RBT notification audio file involves eliminating the unwanted characteristics of the RBT notification audio file such as clicks, pops, breath sound, spacing between the words to ensure smooth flow and the likes.

The processed RBT notification audio file is then saved as Windows PCM format or encoded in mu-law (GSM) /A-law (CDMA) which is a recommended format for audio transmission in a telecommunication network. It will apparent to a person skilled in the art that other supporting formats may also be used to save the processed RBT notification audio file without deviating from the scope of the invention.

According to an embodiment of the invention, the final specifications of the processed RBT notification audio file, when encoded in mu-law (GSM) /A-law (CDMA), are as follows: Bit rate: 64 kbps Sample size: 8bit Channels: 1(mono) Sample rate: 8 KHz

When the processed RBT notification audio file is saved in Windows PCM format, the specification of the process file is as follows: Bit rate: 128 kbps Sample size: 16bit Channels: 1(mono) Sample rate: 8 KHz

Although the procedure for processing an RBT notification audio file has been disclosed, it will be apparent to a person skilled in the art that other audio file may be processed using same or similar procedure without deviating fro the scope of the invention. Other audio files may include prompts, notifications, messages, advertisements, commentary, and the likes. The processing of these audio files are executed using a combination of one or more steps of FIGs. 5A, 5B, and 5C. Apart from the steps of the method as described in conjunction with FIGs. 5A, 5B, and 5C, other steps like cleaning the audio file may also be included for processing audio files.

FIG. 6 is a flowchart depicting the steps involved in creating a hybrid RBT audio file in a telecommunication network in conjunction with an embodiment of the invention.

At step 602, the RBT audio file is processed as discussed in conjunction with FIGs. 5A, 5B, and 5C. At step 604 the RBT notification audio file is processed as discussed above. The final specifications of the RBT audio file and the RBT notification audio file is in coherence with each other. At step 604, the RBT audio file and the RBT notification audio file are integrated to generate a hybrid RBT audio file. According to an embodiment of the invention, step 604 comprises the following sub- steps: First the processed RBT audio file is played for a pre-specified period of time. Then the RBT audio file is faded out by gradually reducing the amplitude of the RBT audio file. Thereafter the RBT notification audio file is played. After the RBT notification file is fully played, the RBT audio file is faded in, i.e., the amplitude to the RBT audio file is gradually increased. The hybrid RBT audio file is then transmitted through the telecommunication network. r

It is understood that while certain forms of this invention have been illustrated and discussed, it is not limited thereto. However, various alterations may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Claims

CLAIMS:

1. A method for processing a ring back tone audio file, the ring back tone audio file being played to a caller in a telecommunication network, the method comprising the steps of: a. down-sampling the ring back tone audio file; b. adjusting the frequency of the ring back tone audio file; c. identifying an average peak value of the ring back tone audio file; d. modifying the amplitude of the ring back tone audio file such that the average peak amplitude value of the ring back tone audio file is equal to a desired amplitude value; and e. applying hard limit to the ring back tone audio file such that the peak amplitude is below a pre-specified amplitude level.

2. The method as recited in claim 1 further comprising the step of receiving audio file modification parameters.

3. The method as recited in claim 2 wherein the audio file modification parameters comprise down sampling parameters, frequency adjusting parameters, dynamic processing parameters.

4. The method as recited in claim 1 wherein the step of adjusting the frequency comprises the step of modifying the frequencies within a pre-specified frequency range.

5. The method as recited in claim 1 further comprising the steps of: a. processing a ring back tone notification audio file; and b. integrating the ring back tone audio file and the ring back tone notification audio file to generate a hybrid ring back tone audio file.

6. A system for processing an ring back tone audio file in a telecommunication network, the system comprises : a. a down-sampler for down-sampling the ring back tone audio file; b. a frequency adjuster for adjusting the frequency of the ring back tone audio file; c. means for identifying an average peak value of the ring back tone audio file; and d. a dynamic processor for processing the amplitude of the ring back tone audio file, the dynamic processor further comprising: means for modifying the amplitude of the ring back tone audio file such that the average peak amplitude value of the ring back tone audio file is equal to a pre-specified amplitude value; and means for applying hard limit to the ring back tone audio file such that the peak amplitude is below a pre-specified amplitude level.

7. The system as recited in claim 6 further comprises means for receiving audio file modification parameters.

8. The system as recited in claim 7, wherein the means for receiving audio file modification parameters comprise means for receiving down sampling parameters, means for receiving frequency adjusting parameters, means for receiving dynamic processing parameter.

9. The system as recited in claim 6 wherein the means for adjusting the frequency of the ring back tone audio file comprises filters for modifying the frequencies within a pre-specified frequency range.

10. The system as recited in claim 1 further comprises of: means for processing a ring back tone notification audio file; and means for integrating the ring back tone audio file and the ring back tone notification audio file to generate a hybrid ring back tone audio file.