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Old 1st December 2012, 07:09 PM   #1
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Default I2S : FS and LR

Newbie question here...

Someone told me recently that FS and LR are the same signal. Why these two designations then?
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Old 1st December 2012, 07:46 PM   #2
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As I have been learning about I2S there seems to be many designations for each line. Not sure why? by LR is the word clock. some times labeled WCLK, or LRCK never seen it labeled FS however. but the i2S wiki shows WS as a possible meaning WORD SELECT line...it is very confusing I agree

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Old 1st December 2012, 07:49 PM   #3
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FS = Frame Sync.
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Old 1st December 2012, 08:46 PM   #4
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I'll explain...

I built a board using a CS8414 as receiver. Basically, SPDIF goes in and I2S goes out: BCK, DATA and FS. However, if I compare it with a USB/I2S converter like the XMOS, there is no FS as output but LR.
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Old 1st December 2012, 10:15 PM   #5
qusp is offline qusp  Australia
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think of LRCK or FS, or WS as your samplerate, because they will always be the same speed as the samplerate; each left/right frame/sample/word.

it comes about because i2s was never developed as an interconnection standard between components for the consumer, but rather for chips on the same PCB, or at the very least part of the same design. there are many variants of i2s, PCM etc. so each manufacturer didnt really have other devices in mind when coming up with the naming.
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Old 2nd December 2012, 12:30 AM   #6
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Thanks qusp for your "clear" answer. Unfortunately, I don't always take the time to thank everyone that helps me on that forum.
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Old 3rd December 2012, 05:38 AM   #7
qusp is offline qusp  Australia
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no problem.
MCLK is your clock speed, not really officially part of the i2s 'standard'
FS/WS/LRCK are all the same thing. you will sometimes see clock speeds defined as 128/256/512 * FS and your dac max sample-rate will be defined by its MCLK and the max multiple
BCK, or SCK is bitclock/sampleclock
SDATA is the music data and you will see this multiplied out for multichannel SDATA1, SDATA2 etc
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Old 10th December 2012, 03:35 PM   #8
jstang is offline jstang  United States
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Best to look at the DAC spec sheet to understand exactly what it is expecting from I2S signals.

As mentioned its not really a standards based spec, but more a de'facto spec.
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