The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Nov. 09, 1999
Filed:
Sep. 17, 1997
Jeffrey Eames Taylor, Bellevue, WA (US);
Microsoft Corporation, Redmond, WA (US);
Abstract
A sample rate converter for converting a digital signal having a particular sample rate frequency into a signal having a different, specified sample rate frequency. The converter includes an interpolation function for increasing the sample rate frequency of the input signal by an interpolation factor (L), so as to produce an intermediate signal having an intermediate sample rate frequency. The intermediate signal is then filtered with a predefined single-stage, low-pass filter to eliminate high frequency noise introduced as a result of the interpolation. The filtered intermediate signal is then supplied to a decimation function, which extracts samples from the intermediate signal in accordance with a decimation factor (M), thereby producing an output signal having the desired sample rate frequency. The filter is configured so as to be optimized to provide the best conversion results for a plurality of critical input/output sample rate conversion pairs, which are used to define the filter cutoff frequency. The converter can be equipped with a single predefined filter, which is then used for all conversions, or the converter can be equipped with a plurality of predefined filters, and the most appropriate filter selected based on the desired level of quality for the conversion. Since the filter is predefined and fixed, there is no need to recalculate the filter every time the converter is executed or when a different input/output rate is specified. In operation, the input signal is interpolated to an intermediate sample rate by inserting L-1 zero value data points between the existing data points. This intermediate signal is then low pass filtered, but the filter skips all of the intervening zero value data points, thereby greatly enhancing the efficiency of the converter. The filtered signal is then decimated, by removing every M-1 out of every M data samples.