I2S : FS and LR

crazyfrog · 1st December 2012, 07:09 PM

Newbie question here...

Someone told me recently that FS and LR are the same signal. Why these two designations then?
Thanks

Zero Cool · 1st December 2012, 07:46 PM

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

I²S - Wikipedia, the free encyclopedia

Ken Newton · 1st December 2012, 07:49 PM

FS = Frame Sync.

crazyfrog · 1st December 2012, 08:46 PM

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.

qusp · 1st December 2012, 10:15 PM

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.

crazyfrog · 2nd December 2012, 12:30 AM

Thanks qusp for your "clear" answer. Unfortunately, I don't always take the time to thank everyone that helps me on that forum.

qusp · 3rd December 2012, 05:38 AM

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

jstang · 10th December 2012, 03:35 PM

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.

1st December 2012, 07:09 PM	#1
crazyfrog diyAudio Member Join Date: May 2009	I2S : FS and LR Newbie question here... Someone told me recently that FS and LR are the same signal. Why these two designations then? Thanks

1st December 2012, 07:46 PM	#2
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	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 I²S - Wikipedia, the free encyclopedia __________________ It's not about what you can BUY...It's about what you can BUILD!

1st December 2012, 07:49 PM	#3
Ken Newton diyAudio Member Join Date: Apr 2003 Location: Eastern Pennsylvania	FS = Frame Sync. __________________ Ken

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1st December 2012, 08:46 PM	#4
crazyfrog diyAudio Member Join Date: May 2009	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.

1st December 2012, 10:15 PM	#5
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	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.

2nd December 2012, 12:30 AM	#6
crazyfrog diyAudio Member Join Date: May 2009	Thanks qusp for your "clear" answer. Unfortunately, I don't always take the time to thank everyone that helps me on that forum.

3rd December 2012, 05:38 AM	#7
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	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

10th December 2012, 03:35 PM	#8
jstang diyAudio Member Join Date: Jun 2008	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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