Method for encoding audio signals

• US 5,649,053 A
• Filed: 07/15/1994
• Issued: 07/15/1997
• Est. Priority Date: 10/30/1993
• Status: Expired due to Term

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Sang-Wook
• Primary Examiner(s): Sheikh, Ayaz R.
• Assistant Examiner(s): EDOUARD, PATRICK NESTOR
• Application Number:
  US08/275,452
• Time in Patent Office: 1,096 Days
• Field of Search: 395/2.38, 395/2.1, 395/2.39, 395/2.35, 395/2, 381/31, 381/29, 381/36, 381/37, 381/30, 381/47, 375/243, 395/2.91, 395/2.92
• US Class Current: 704/229
• CPC Class Codes: H04B 1/665 using psychoacoustic properties of the ear, e.g. masking effect

Abstract

In allocating the number of quantization bits in a method for encoding audio signal using the characteristics of human auditory system, the encoding method improves operation speed by allocating quantization bits sequentially from highest frequency bands to lowest frequency bands, thereby enabling non-iterative operation, which reduces the number of operations.

Claims

1. A method of encoding an audio signal comprising the steps of:

sampling a time-domain audio signal;

converting said sampled audio signal into a frequency-domain signal divided into a plurality of critical bands;

allocating to each critical band the number of quantization bits allowing the NMR (noise-to-mask ratio) for the corresponding critical band to be minimum;

quantizing a frequency-domain-signal by the allocated number of quantization bits;

wherein in said bit allocating step, quantization bits are allocated according to the weight of critical bands in the order from the critical band having the highest frequency to the one having the lowest frequency and the number of quantization bits allocated to an arbitrary critical band is determined by the weight of said critical band among the critical bands which are equal to or below said critical band.

2. A method of encoding an audio signal as claimed in claim 1, wherein the weight of an arbitrary critical band is determined by the magnitude of the signal-to-masking threshold ratio (SMR) of said arbitrary critical band among the critical bands which are equal to or below said arbitray critical band.

3. A method of encoding an audio signal comprising the steps of:

sampling a time-domain audio signal;

converting said sampled audio signal into a frequency-domain signal divided into a plurality of critical bands;

allocating to each critical band the number of quantization bits allowing the noise-to-mask ratio ("NMR") for the corresponding critical band to be minimum and according to the weight of critical bands in the order from the critical band having the highest frequency to the one having the lowest frequency, wherein the number of quantization bits allocated to an arbitrary critical band is determined by the following formula, in consideration of the magnitude of signal-to-masking threshold ratio (SMR) of said arbitrary critical band among the critical bands which are equal to or below said arbitrary critical band;

##EQU2## where BIT_i is the number of quantization bits allocated to an arbitrary critical band, BIT_total is the number of quantization bits which can be allocated to the critical bands which are equal to or below said arbitrary critical band, SMR_i is the SMR of said arbitrary critical band, SMR_min is the minimum SMR among SMRs of the critical bands which are equal to or below said arbitrary critical band, and SMR_total is the total of SMRs of the critical bands which are equal to or below said arbitrary critical band, and N is the number of bands; and

quantizing a frequency-domain-signal by the allocated number of quantization bits.

4. A method of encoding an audio signal comprising the steps of:

sampling a time-domain audio signal;

converting said sampled audio signal into a frequency-domain signal divided into a plurality of critical bands;

allocating to each critical band the number of quantization bits allowing the NMR for the corresponding critical band to be minimum;

quantizing a frequency-domain-signal by the allocated number of quantization bits;

wherein in said bit allocating step, quantization bits are allocated according to the weight of critical bands in the order from the critical band having the highest frequency to the one having the lowest frequency and the number of quantization bits allocated to an arbitrary critical band is compared with the new number of needed bits (NEEDBIT_new) determined by the below formula, the number of quantization bits is allocated to the corresponding critical band if said quantization bit number is greater than or equal to the new number of needed bits, and the number of quantization bits is not allocated to the corresponding critical band if said quantization bit number is smaller than the new number of needed bits;

space="preserve" listing-type="equation">NEEDBIT.sub.new =W.sub.i ×

NEEDBIT=W.sub.i (S+BIT.sub.min)

where W_i is a characteristic weight of each critical band, NEEDBIT is the used number of needed bits, S is the scalefactor, and BIT_min is the minimum number of bits used for quantization.