JP2844944B2 - Sampling frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a sampling frequency converter of an audio signal processing device. In particular, the present invention relates to a sampling frequency converter that inputs digital audio data and generates digital audio data having a sampling frequency different from the input sampling frequency.

[0002]

2. Description of the Related Art Conventionally, a sampling frequency converter converts input digital audio data into analog audio data once, samples the converted analog audio data at a required sampling frequency,
A first method for generating new digital voice data;
A second method of using a digital filter and performing linear interpolation at the least common multiple of two different sampling frequencies to generate data at the required sampling frequency;
A digital filter is connected in a cascade, a double method of generating sampling data, and a third method of generating data of a required sampling frequency is employed.

[0003]

However, in such a conventional sampling frequency converter, when returning to the analog audio data of the first method once, the S / N (signal-to-noise) due to the accumulation of quantization noise is obtained. Ratio), quality deterioration due to aging of the constituent elements, and quality deterioration due to an increase in the number of adjustment points of the analog circuit.

In the case of using the digital filter of the second method, the fact that the least common multiple of two different sampling frequencies is determined in advance means that the relationship between the two sampling frequencies is determined in advance (nf _s1 = m
f ₁ ), and there was a disadvantage that only the value could be converted.

When the digital filters of the third method are connected in cascade, the number of connection stages is different due to an increase in delay due to the cascade connection and a relationship between two different frequencies. However, there is a disadvantage that the circuit cannot be increased and the circuit becomes large.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks, reduces errors in data interpolation, generates audio data having a local sampling frequency different from the input sampling frequency, and has a highly stable sampling frequency conversion. It is an object of the present invention to provide a sampling frequency converter capable of performing the following.

[0007]

According to the present invention, there is provided a clock generator for synchronizing with an input sampling frequency and generating a first clock frequency of n times the frequency, inputting audio data and setting the first clock frequency to the first clock frequency. A first digital filter that calculates n synchronized interpolation data, a counter that divides the first clock frequency by n to generate a second clock frequency, and outputs a second clock frequency of the counter. A comparator for comparing a phase with an input local sampling frequency and outputting a phase control signal, wherein the counter includes means for controlling a count based on the phase control signal, and the output of the counter is a second clock frequency. A latch for latching the output interpolation data of the first digital filter on the basis of Characterized by comprising a resampling unit for resampling on the basis of the ring frequency.

In addition, a second digital filter for removing noise from the output of the resampling means based on the local sampling frequency can be provided.

[0009]

The clock generator synchronizes with the input sampling frequency and generates a first clock frequency of n times the frequency. The first digital filter inputs audio data and calculates n pieces of interpolation data synchronized with the first clock frequency. The counter generates a second clock frequency by dividing the frequency of the first clock signal by n. The comparator compares the phase of the output second clock frequency of the counter with the input local sampling frequency and outputs a phase control signal. The counter controls the count based on the output phase control signal of the comparator. The retainer latches the output interpolation data of the first digital filter based on the output second clock frequency of the counter. The resampling means resamples the output of the retainer based on a local sampling frequency.

The second digital filter can remove noise from the output of the resampling means based on the local sampling frequency.

As described above, the error of the data interpolation can be reduced, audio data having a local sampling frequency different from the input sampling frequency can be generated, and the sampling frequency can be converted with high stability.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a sampling frequency converter according to an embodiment of the present invention. In Figure 1, the sampling frequency converter includes a clock generator 2 for generating a clock frequency nf _s1 as the first clock frequency in synchronization n times the frequency to the sampling frequency f _s1 as a sampling frequency to be input, audio data D _in a digital filter 1 as a first digital filter for calculating n number of interpolation data DI _n synchronized input clock frequency nf _s1 the clock frequency f of the clock frequency nf _s1 as a second clock frequency by divide-by-n a counter 4 that generates _s2, comparator 5 outputs an advance signal P _S or delay signal D _s as compared with the phase of the local sampling frequency f ₁ phase control signal input and output clock frequency f _s2 of the counter 4 with the door, the counter 4 is based on the output lead signal P _s or delayed signal D _s of the comparator 5 counts It comprises means for controlling the output clock frequency f of the counter 4
Output interpolation data DI of digital filter 1 based on _S2
a retainer 3 for latching the _n, there the output of the retainer 3 in that an output retainer 6 as resampling means for resampling on the basis of the local sampling frequency f _1.

The operation of the sampling frequency converter having such a configuration will be described.

[0014] In FIG 1, the audio data D _in sampled at the sampling frequency f _s1 is supplied to the clock generator 2 and the digital filter 1 to generate an n times the clock frequency nf _s1 synchronized with the sampling frequency f _s1 . The digital filter 1 includes a clock generator 2
More of n synchronized with the clock frequency nf _s1 interpolated data DI _n (provided that one of the n even be using the voice data D _in the input) is calculated, and supplies to the retainer 3. Also, the clock frequency nf from the clock generator 2
_s1 is supplied to the counter 4, the counter 4 generates a clock frequency f _s2 synchronized with the sampling frequency f _s1 , and based on the clock frequency f _s2 , the retainer 3 converts one of the inputted interpolation data DI _n data. Hold.

On the other hand, the clock frequency f _s2 is supplied to a comparator 5 where the phase is compared with the local sampling frequency f ₁ . The comparator 5 compares the phase of the clock frequency f _s2 with the phase of the local sampling frequency f _1, and determines whether the advance signal P _S or the lag signal D _S (for example, the clock frequency f _s2 is higher than the local sampling frequency f _1). If it is present, or delay if it is late) and supplies it to the counter 4. The counter 4 outputs the advance signal P _S
When the delay signal D _S arrives, the count is delayed, and when the delay signal D _S arrives, the count is advanced. This makes almost close phase and clock frequency f _s2 and local sampling frequency f _1. For this reason, the output of the holder 3 held at the clock frequency f _s2 changes at a phase almost close to the local sampling frequency f ₁ , and the output holder 6 re-latches at the local sampling frequency f _1. it can, it is possible to obtain the output data D _O.

FIG. 2 is a block diagram of a sampling frequency converter according to another embodiment of the present invention. Through a digital filter 7 the output of the output retainer 6 as shown in FIG. 2, the digital audio data synchronized by performing filtering on the local sampling frequency f _1, the local sampling frequency f ₁ which removes unnecessary noise components D
You can get _out .

[0017]

As described above, according to the present invention, it is possible to reduce errors in data interpolation, generate audio data having a local sampling frequency different from the input sampling frequency, and perform sampling frequency conversion with high stability. There is an excellent effect that can be done.

[Brief description of the drawings]

FIG. 1 is a block diagram of a sampling frequency converter according to an embodiment of the present invention.

FIG. 2 is a block diagram of a sampling frequency converter according to another embodiment of the present invention.

[Explanation of symbols]

1 the digital filter 2 clock generator 3 cage 4 counter 5 comparator 6 outputs the cage 7 digital filter D _in the audio data D _O output data D _out digital audio data D _S delayed signal P _s advance signal f ₁ local sampling frequency nf _s1 , _fs2 clock frequency

Claims (2)

(57) [Claims] 1. Synchronizing with an input sampling frequency, n
A clock generator for generating a first clock frequency of twice the frequency, a first digital filter for calculating n pieces of interpolation data synchronized with the first clock frequency based on input audio data, And a comparator that compares the phase of the output second clock frequency of the counter with the input local sampling frequency and outputs a phase control signal. The counter includes means for controlling the count based on the output phase control signal of the comparator, and holds the output interpolation data of the first digital filter based on the second clock frequency output from the counter. And a resampling unit for resampling the output of the retainer based on the local sampling frequency. Sampling frequency converter characterized by comprising a stage. 2. The sampling frequency converter according to claim 1, further comprising a second digital filter for removing noise from an output of said resampling means based on said local sampling frequency.