| Sample rate conversion combined with filter -> Monitor Keywords |
|
|
 
Sample rate conversion combined with filterSample rate conversion combined with filter description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070146176, Sample rate conversion combined with filter. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a method and apparatus for performing sample rate conversion. In particular, the present invention is directed toward a technique and apparatus for combining digital sample rate conversion with digital filtering. BACKGROUND OF THE INVENTION [0002] Sample-rate conversion (SRC) refers to the process of translating a sequence of discrete data samples with a certain sampling rate into another sequence with a different sampling rate, while preserving the information contained in the original sequence. Sample rate conversion can be a relatively simple technique where the two sample rates are related by a fairly small integer ratio. For example, if the ratio of sample rates is 4:5, the input signal only needs to be upsampled by a factor of four and then, after appropriate filtering, down-sampled by a factor of five. [0003] FIG. 1 illustrates an example of such a Prior Art sample rate conversion technique. In this Prior Art embodiment, input data may be upsampled by a factor of M in upsampler 110, to produce an upsampled data stream. Upsampling may comprise the process of creating new intermediate samples by inserting samples of value zero as intermediate values. Upsampled data may be filtered in low pass filter 120, which may comprise a digital filter. The resultant data may be downsampled by a factor of N in downsampler 130 which may decimate unwanted data samples. Downsampling may comprise decimating (eliminating) intermediate sample values to create a new sample set at the desired output sample rate. [0004] Low pass filter 120 may be used to eliminate spectral "images" produced when upsampling. Such images are illustrated in FIG. 2. Referring to FIG. 2, the sample data at rate fs is illustrated, along with image data produced during upsampling at sample rates 2 fs and 3 fs. FIG. 3 illustrates how filtering may be used to eliminate undesirable images while preserving desirable data, as illustrated in FIG. 4 to produce sample rate converted data as illustrated in FIG. 5. [0005] In the example given above for a ratio of sample rates of 4:5, M would equal 4 and N would equal 5. Such a Prior Art sample rate conversion technique may be suitable for relatively simple rate conversions. However, not all scenarios where sample rate conversion is desired have such simple sample rate ratios. For example, when converting by more drastic ratios (e.g., 124:359) the amount of processing required to upsample and then downsample may be prohibitive. [0006] As compared to the simpler scenario where the sampling rates are related by a relatively simple ratio, the term "asynchronous sample-rate conversion" is often used to signify situations where the ratios are rather ill-defined numbers such that their least common multiple is a very large number. Asynchronous sample rate conversion is particularly applicable in cases where data is at the "same" sampling rate, but created with a different clock crystal, and thus at a slightly different sampling frequency. Thus, one set of data might have a sample rate of a "fast" 48 KHz and another might have a sample rate of a "slow" 48 KHz. Such ratios like this that are close to 1:1, but not exact, fall into the category of "asynchronous sample-rate conversion." Asynchronous sample-rate converters are commonly used when bridging two systems that are on different sampling rates and/or master operating clocks. [0007] Additionally, in the field of audio, there are various standards that utilize different sampling rates such as 32 KHz, 44.1 KHz, 48 KHz, and so on, and sample rate converters are commonly used to interconnect different systems with the different standards. [0008] There are times when a digital data stream needs to be converted to a different sampling frequency and in addition, be filtered in some way. One way to accomplish this task would be to have a sample rate conversion block followed by (or preceded by) a filter block. Such a setup would look like one of the block diagrams illustrated in FIG. 10. In the two Prior Art embodiments of FIG. 10, an input signal u(k) 1710 may be fed to a sample rate converter 1720 and a digital filter 1730, in either order depending upon which side of the SRC the filtering is performed. Sample rate converter 1720, as discussed previously herein, alters the sample rate of the digital input data u(k) to a different sampling rate than the input signal, and may be either synchronous or asynchronous. Digital filter 1730 may perform a number of digital filtering operations as desired by a user to alter the input signal. Output signal y(k) is thus suitably filtered and converted for a desired end use. [0009] Applications for such sample rate conversion and digital filtering are relatively common, particularly in the digital audio arts. The Prior Art solutions of FIG. 10, while intuitive, require separate components and/or software for the digital filtering and sample rate conversion steps. Given that both functions may be required in a number of applications, it would be advantageous to combine both functions into one system, to reduce the complexity of hardware and/or software. SUMMARY OF THE INVENTION [0010] In the present invention, the digital filtering and sample rate conversion blocks are combined in order to reduce hardware and/or computational complexity. The present invention accomplishes both tasks using a novel filter design to perform sample rate conversion. The filter may also be used to perform other digital filtering functions, thus providing a single hardware/software technique to perform both functions. [0011] In the present invention, the process of sample rate conversion may be combined with another digital filter. Two embodiments may be used to achieve this function. In a first embodiment, the filter may be clocked at the output data rate (i.e., the data rate after rate conversion). In a second embodiment, the filter may be clocked at the input data rate (i.e., the data rate before rate conversion). In both cases, the filter's structure is modified in a novel way to handle the rate conversion. The present application is directed toward a sample-rate conversion filter using the output data rate clock as the filter clock. [0012] The technique of the present invention may be used to modify any low pass Infinite Impulse Response (IIR) filter with SRC modification terms to remove spectral images that are associated with sample rate conversion--without increasing the number of states in the original filter. Thus, an IIR filter used for other filtering purposes (e.g., audio processing or the like) can double as a sample rate converter, based on this invention. [0013] The present invention includes a method of converting input data samples provided at a first sample rate to output data samples at a second sample rate unequal to the first sample rate. An IIR filter, whose internal states are updated at the second sample rate, filters the input data samples to produce output data samples at the second sample rate. If a new input sample arrives at a time differing from the update of the IIR filter's internal states, then at least one internal state of the Infinite Impulse Response filter may be modified to account for the time difference. [0014] In some implementations, at least one internal state of the IIR filter is modified only when the input value changes when the input arrives at a time different from the update of the IIR filter's internal states. In other implementations, at least one internal state of the IIR filter is always modified when the input arrives at a time different from the update of the IIR filter's internal states, regardless of whether the input changes value at that time. [0015] In a preferred embodiment, the input changes value no more than once between updates of the IIR filter's internal states. [0016] The IIR filter's internal states may comprise a vector X representing current states, vector X' representing what those states will be at the next point in time, vector U representing an input to the filter, and vector Y representing output of the filter, and matrices A, B', C, and D determine how the internal states are updated and how outputs are made from the internal states, wherein state variable descriptions are represented as X'=AX+B'U Y=CX+DU X=z.sup.-1X' wherein the B' matrix may comprise a column matrix whose elements are polynomials in z.sup.-1. Furthermore, the polynomials in the B' matrix may be of increasing degree with respect to the coefficients of z.sup.-1. [0017] In one embodiment, the sample rate conversion technique of the present invention may be combined with integer interpolation or decimation stages in order to achieve further sample rate conversion. This embodiment may be useful to guarantee that the input changes value no more than once between updates of the IIR filter's internal states. It may also be useful since creating a higher sampling rate into the IIR filter generally reduces the complexity or accuracy required of the SRC modification term(s). BRIEF DESCRIPTION OF THE DRAWINGS [0018] FIG. 1 is a block diagram illustrating how traditional sample rate conversion is performed. [0019] FIG. 2 is a spectrum diagram illustrating the resulting data and artifacts produced after upsampling the input digital signal. [0020] FIG. 3 is a spectrum diagram illustrating the resulting data and artifacts produced after upsampling the input digital signal, highlighting the desired data portion of upsampled digital signal. Continue reading about Sample rate conversion combined with filter... Full patent description for Sample rate conversion combined with filter Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Sample rate conversion combined with filter patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Sample rate conversion combined with filter or other areas of interest. ### Previous Patent Application: Transmission system and method Next Patent Application: Sample rate conversion combined with filter Industry Class: Coded data generation or conversion ### FreshPatents.com Support Thank you for viewing the Sample rate conversion combined with filter patent info. IP-related news and info Results in 0.13138 seconds Other interesting Feshpatents.com categories: Electronics: Semiconductor , Audio , Illumination , Connectors , Crypto , 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
