Blank detector for cassette tape player
AssigneeFord Motor Company
InventorsFrank M. Hirschenberger, John E. Whitecar, Nicholas L. Difiore
Life of this patent
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Abstract
Digital signal processing (DSP) employing a differential mean calculation automatically distinguishes sections of blank tape from program material (such as music or voice) on cassette tapes. Blank tape produces a negligible differential mean value while program material produces substantial differential mean values. Thus, each differential mean is compared to a threshold so that a cassette player can be commanded to fast forward through a blank section of tape. A music envelope detector insures that low amplitude music signals are not detected as blank.
Claims19
Apparatus for detecting the absence of information in a channel used to carry an information signal comprising:
- an averager for averaging said channel signals over a first and a second time period to form first and second averages, said first and second time periods having respective lengths minimizing the variance in mean Gaussian noise without minimizing the variance corresponding to said information signal;
- a subtractor for forming a difference between said first and second averages;
- and
- a first comparator for detecting said absence of information when said difference is below a predetermined threshold.
An audio cassette player comprising:
- a multi-channel cassette tape deck for reproducing first and second audio signals from a cassette tape;
- an analog-to-digital converter digitizing said first and second audio signals;
- a first summer receiving said first and second audio signals to produce a sum signal;
- an N-sample averager periodically generating average signals over N samples of said sum signal;
- a delay block for delaying one of said average signals;
- a second summer receiving an average signal from said N-sample averager and a delayed average signal from said delay block to produce a difference signal;
- and
- a first comparator responsive to said difference signal and a predetermined threshold for detecting an instantaneous blank on said cassette tape.
A method for detecting a blank on a cassette tape reproducing right and left stereo audio signals, said method comprising the steps of:
- sampling said right audio signal to generate an R(i) signal, where i is a sample number;
- sampling said left audio signal to generate an L(i) signal;
- forming a tape level signal DATA(i) according to the formula
- DATA(i)=.vertline.R(i)-R.sub.DC .vertline.+.vertline.L(i)-L.sub.DC .vertline.
- where R.sub.DC and L.sub.DC are DC offset values for said R(i) and L(i) signals, respectively;
- forming a first average tape level signal AVG1 over a first time period according to the formula ##EQU4## where N is a whole number of samples coinciding with said first time period;
- forming a second average tape level signal AVG2 over a second time period according to the formula ##EQU5## where M is a whole number of samples coinciding with said second time period;
- forming a difference signal DIF according to the formula
- DIF=.vertline.AVG1-AVG2.vertline.
- and;
- detecting said blank when DIF is less than a threshold.
A method for detecting the presence of a recorded signal on a cassette tape comprising the steps of:
- sampling a tape signal from said cassette tape:
- generating a plurality of average signals spanning a predetermined envelope time, each of said average signals including a predetermined number of samples of said tape signal;
- generating a plurality of difference signals between a predetermined one of said average signals and each remaining one of said average signals;
- comparing each of said difference signals with a predetermined threshold;
- and
- indicating the presence of a recorded signal if any one of said difference signals is above said predetermined threshold.
Dependencies are inferred from the claim text.