Method of making a window type decision based on MDCT data in audio encoding

1. A method of execution by a computer, the method comprising:

detecting an indication of a transition from a steady signal to a transient signal in a next frame of audio data;

deciding that a preliminary window type of the next frame is a short window type; and

determining a window type of a current frame of data based on the preliminary window type of the current frame and a window type of a previous frame of data, the determination of the window type of the current frame favoring use of a long window type over use of the short window type, wherein the audio data is transformed into a frequency domain using a transformation range defined by the window type.

2. The method of claim 1 wherein detecting an indication of a transition comprises:

computing a plurality of Modified Discrete Cosine Transform (MDCT) coefficients for a current frame of data and a plurality of preliminary MDCT coefficients for a next frame of data using a long window type for each of the current frame and the next frame;

computing a total energy of the current frame using the plurality of preliminary MDCT coefficients of the current frame;

computing a total energy of the next frame using the plurality of preliminary MDCT coefficients of the next frame;

scaling the total energy of the current frame and the total energy of the next frame in logarithmic way;

calculating a gradient energy by subtracting the scaled total energy of the current frame from the scaled total energy of the next frame;

determining whether the gradient energy exceeds a threshold value; and

if the gradient energy exceeds the threshold value, deciding that the transition to the transient signal is likely to occur in the next frame.

3. The method of claim 2 wherein the plurality of preliminary MDCT coefficients is computed from a plurality of corresponding samples produced along the time axis.

4. The method of claim 2 wherein the threshold value is experimentally determined.

5. The method of claim 2 further comprising:

if the gradient energy does not exceed the threshold value,

deciding that the transition to the transient signal does not occur in the next frame, and

deciding that the preliminary window type of the next frame is a long window type.

6. The method of claim 1 wherein determining a window type of a current frame of data based on the preliminary window type of the next frame and a window type of a previous frame of data comprises:

identifying the window type of the previous frame; and

selecting a window type for the current frame to transition from the window type of the previous frame to the preliminary window type of the next frame, the selection favoring the use of the long window type over the use of the short window type.

7. The method of claim 6 wherein selecting a window type for the current frame comprises:

selecting a long window type for the current frame if the preliminary window type of the next frame is a long window type and the window type of the previous frame is any one of a long window type and a short-long window type.

8. The method of claim 6 wherein selecting a window type for the current frame comprises:

selecting a short-long window type for the current frame if the preliminary window type of the next frame is a long window type and the window type of the previous frame is any one of a short window type and a long-short window type.

9. The method of claim 6 wherein selecting a window type for the current frame comprises:

selecting a long-short window type for the current frame if the preliminary window type of the next frame is a short window type and the window type of the previous frame is any one of a long window type and a short-long window type.

10. The method of claim 6 wherein selecting a window type for the current frame comprises:

selecting a short window type for the current frame if the preliminary window type of the next frame is a short window type and the window type of the previous frame is any one of a short window type and a long-short window type.

11. A computer readable medium that provides instructions, which when executed on a processor cause the processor to perform a method comprising:

detecting an indication of a transition from a steady signal to a transient signal in a next frame of data; and

deciding that a preliminary window type of the next frame is a short window type; and

determining a window type of a current frame of data based on the preliminary window type of the current frame and a window type of a previous frame of data, the determination of the window type of the current frame favoring use of a long window type over use of the short window type.

12. The computer readable medium of claim 11 wherein the plurality of preliminary MDCT coefficients is computed from a plurality of corresponding samples produced along the time axis.

13. The computer readable medium of claim 11 wherein the method further comprises:

if the determined window type of the current frame is the long window type, using the plurality of preliminary MDCT coefficients of the current frame as the plurality of final MDCT coefficients of the current frame.

14. A computerized system comprising:

a memory; and

at least one processor coupled to the memory, the at least one processor executing a set of instructions which cause the at least one processor to

detect an indication of a transition from a steady signal to a transient signal in a next frame of data,

decide that a preliminary window type of the next frame is a short window type, and

determine a window type of a current frame of data based on the preliminary window type of the current frame and a window type of a previous frame of data, the determination of the window type of the current frame favoring use of a long window type over use of the short window type.

15. The system of claim 14 wherein the plurality of preliminary MDCT coefficients is computed from a plurality of corresponding samples produced along the time axis.

16. The system of claim 14 wherein the processor is further to use the plurality of preliminary MDCT coefficients of the current frame as the plurality of final MDCT coefficients of the current frame if the determined window type of the current frame is the long window type.

17. An apparatus comprising:

means for detecting an indication of a transition from a steady signal to a transient signal in a next frame of audio data; and

means for deciding that a preliminary window type of the next frame is a short window type; and

means for determining a window type of a current frame of data based on the preliminary window type of the current frame and a window type of a previous frame of data, the determination of the window type of the current frame favoring use of a long window type over use of the short window type, wherein the audio data is transformed into a frequency domain using a transformation range defined by the window type.