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Cadence Generator for 48K and 44.1Hz based Frame Frequencies

IP.com Disclosure Number: IPCOM000019525D
Publication Date: 2003-Sep-17
Document File: 4 page(s) / 216K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a cadence generator that creates various frequencies on the link. Benefits include a programmable 44.1K sequence, and flexibility when designing storage buffers within the Codec.

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Cadence Generator for 48K and 44.1Hz based Frame Frequencies

Disclosed is a method for a cadence generator that creates various frequencies on the link. Benefits include a programmable 44.1K sequence, and flexibility when designing storage buffers within the Codec.

Background

Currently, common sample rates are integral multiples (or submultiples), either 48 kHz or 44.1 kHz standard base rates. If a codec supports sample rates using a base rate of 44.1 kHz, then it must be derived as an exact 147/160 mathematical multiple of the 48.0 kHz base rate. Table 1 shows all the sample rates defined with their multiples and base rates.

 

 

48.0

44.1

Base rate

Multiple

 

 

 

 

1/6

 

8.0

 

 

1/4

 

 

11.025

 

1/3

 

16.0

 

 

1/2

 

 

22.05

 

2/3

 

32.0

 

 

1

 

48.0

44.1

 

2

 

96.0

88.2

 

4

 

192.0

176.4

 

                                 Table 1

Since the link runs at a fixed base rate of 48 kHz, delivery timings for streams with sample rates of 48 kHz are straight forward. The base rate sample defines the number of complete sample blocks that must be transmitted in each frame. For every input or output, , ‘y’ complete sample blocks are transmitted on the link on every nth frame, as shown in Table 2.

 

 

y
number of samples

n
Frame Frequency

Multiple

 

 

 

1/6

 

1

6

1/4

 

1

4

1/3

 

1

3

1/2

 

1

2

2/3

 

2

3

1

 

1

1

2

 

2

1

4

 

4

1

                                 Table 2

Since the link frame rate is fixed at 48 kHz, streams using a basic rate of 44.1 kHz must transmit on a cadence using a lower aggregate transmission rate to match the lower base rate. For streams running at a sample rate of 44.1 kHz, there are occasional frames that will not contain a sample, generating a cadence where out of every 160 frames, 13 frames will not contain a sample. For example:

         12-11-11-12-11-11-12-11-11-12-11-11-11-(repeat)

Following the empty frame at the end, the cadence repeats itself continuously; it generates exactly 147 sample blocks every 160 frames and avoids any long-term drift between sample delivery and the rendering clock. For streams running at multiples or sub-multiples of 44.1 kHz, this cadence is applied using the frame frequency rules from Tables 1 and 2.

General Description

The disclosed method consists of two parts: logic A and logic B (see Figure 1). Logic A generates a stream-valid signal each frame when running in 48 kHz mode, based on the required frequency. Logic B is shut off in 48 kHz mode. When in 44.1 kHz mode, both A and B are active; logic A still generates the stream-valid signal for various subs; however, selective valid streams are blocked by logic B based on the cadence for various 44.1k rates. The cadence generator is associated with each output. Therefore, four cadence generators are needed for four streams.

Various sample rates of ½, ⅓, ¼, and 1/6 can be obtained by running the link at 48 kHz and selectively sampling the link based on the sub. For the 48 kHz sample rate, a valid stream in each frame is needed. However, if the sample rate is halved a valid stream is needed in only half the number of frames (i.e. every other frame).

Logic A generates the stream-valid signal dur...