There haven't been any threads about Cirrus/Crystal's new CS8421 high-resolution ASRC, so I thought I'd start one.
This looks like a very impressive part. 175dB dynamic range and the ability to output 32 bit PCM data. Naturally there isn't a serious use for 32 bit PCM unless you're doing DSP work, but this suggests that the part's internal arithmetic is relatively high precision.
The specs of this part are better than TI/Burr-Brown's SRC4192 (which is rumored to have problems in its current first revision) and better than the AD1896.
Does anyone have any experience using this part yet?
This looks like a very impressive part. 175dB dynamic range and the ability to output 32 bit PCM data. Naturally there isn't a serious use for 32 bit PCM unless you're doing DSP work, but this suggests that the part's internal arithmetic is relatively high precision.
The specs of this part are better than TI/Burr-Brown's SRC4192 (which is rumored to have problems in its current first revision) and better than the AD1896.
Does anyone have any experience using this part yet?
Wodgy said:
I was wondering when someone was going to spot that
little puppy!
What would be helpful is a plot of internal jitter rejection
low pass function. TI didn't specify this either.
I'll see if I can get some info out of Cirrus WRT this.
ASRC's are definately coming of age that's for sure.
I wish they could get their act together WRT ADC chips
which appear to be the comparative weakest link in chain
and that's the place where a bit more DR would come in
handy.
Cheers,
Terry
Re: Re: Any feedback on new CS8421 high-res ASRC?
I've heard that the current revision of the TI's part has relatively poor internal jitter rejection, despite the claim on the first page of the datasheet. It would be great to see actual measurements though. (Apparently TI may also be working on a revision "B" of the SRC4192.)
Let us know what you find out. I'd love to see that info.
Terry_Demol said:
I've heard that the current revision of the TI's part has relatively poor internal jitter rejection, despite the claim on the first page of the datasheet. It would be great to see actual measurements though. (Apparently TI may also be working on a revision "B" of the SRC4192.)
Let us know what you find out. I'd love to see that info.
I thought about using it in a new DAC project i'm working on - it's a cheap chip with incredible specs. I chose an AD1896 instead, based on:
- you can't buy the CS8421 anywhere (yet)
- the 2.5V supply requires a separate LDO + capacitors + etc, which take up board space and increase the implemented price of the chip.
- no digital PLL / jitter rejection data is available.
Hopefully issues #1 and #3 will fix themselves soon. If I had 2.5V already on the board, I wouldn't care as much about #2.
- you can't buy the CS8421 anywhere (yet)
- the 2.5V supply requires a separate LDO + capacitors + etc, which take up board space and increase the implemented price of the chip.
- no digital PLL / jitter rejection data is available.
Hopefully issues #1 and #3 will fix themselves soon. If I had 2.5V already on the board, I wouldn't care as much about #2.
Hi,
I can’t comment on the CS8421 but lets hope it sounds better then the earlier CS8420 - which sounds truly terrible - I used on an Digital amplifier Eval board - where it could be "bypassed" it’s a really lousy sounding device – completely collapses / compresses the sound stage, destroys LF rhythm….
After my experience of CS8420 SRC, I’m very weary of any SRC – although I’m designing a product that uses the Ti device – although it can be bypassed when the unit is Clock-Locked to a transport – it will be interesting to compare both modes of operation.
John
I can’t comment on the CS8421 but lets hope it sounds better then the earlier CS8420 - which sounds truly terrible - I used on an Digital amplifier Eval board - where it could be "bypassed" it’s a really lousy sounding device – completely collapses / compresses the sound stage, destroys LF rhythm….
After my experience of CS8420 SRC, I’m very weary of any SRC – although I’m designing a product that uses the Ti device – although it can be bypassed when the unit is Clock-Locked to a transport – it will be interesting to compare both modes of operation.
John
SRC4192 vs CS8421
For what it's worth:
Preamble
An asynchronous SRC (and I mean *any* asynchronous SRC) always sees two sources of jitter at its input. One is the jitter of the input signal itself, which is what people have in mind when they expect an SRC to solve it. The second is jitter caused by resampling the input clock to its master clock (which may be linked to the output frequency or even a third clock source, in which case the output sampling frequency will be a second source of such errors). The SRC "sees" the input sampling rate only in intervals dictated by its master clock. In most realistic cases this jitter source will actually dominate.
Jitter and PLL modes
The TI SRC4192 has several PLL settings among which it chooses depending on the amount of jitter present on the input. For normally low amounts (anything we'd practically encounter) of jitter, it has a narrow mode where the ratio estimation register is updated only once every few seconds. This means that between updates the conversion factor is held absolutely constant (ie it operates like a synchronous src), and none of the input jitter makes it to the output at all.
If the jitter is too high for the input fifo to hold it (this fifo is rather short because delay was a design criterion), the PLL reverts to a more traditional mode of operation and the chip will indeed encode the input jitter (albeit attenuated) into the output signal as phase modulation of the audio.
I haven't actually measured the CS8421. However, I find graphs like 24b (see data sheet) telling. There are clear side bands around the test signal. This clearly shows leftovers from the quantisation effect described in the preamble.
By its trick of sampling every few (say 4) seconds, the TI chip insures all of these effects are relegated to an area 0.125Hz wide (where they are arguably quite innocuous), whereas the CS8421 has only a lowpass filter and does pass jitter up to significant frequencies. Since this jitter was actually only created by the SRC process itself, you may actually be worse off after SRC than before.
Filtering
Another point of interest is the filtering. The CS8421 shows some minor images in some of the FFT graphs, but on the other hand has pretty much no inband ripple (and hence less pre- and post-echos) than does the SRC4192. It seems someone has heard my (and other people's) pleas for better inband behaviour, which at this level of performance is probably more important than a minor outband spur.
Interpolation
The actual interpolation process appears to be impeccable on both chips, none of them showing any interpolation related spuriae.
Conclusion?
The CS8421 just misses the mark due to the passing of newly created jitter (again something all ASRCs have to contend with, but something which the TI chip addresses elegantly).
The gripe I have with the TI chip is its inband ripple.
Up to you to pick which you think Hz least.
Cheers,
Bruno
For what it's worth:
Preamble
An asynchronous SRC (and I mean *any* asynchronous SRC) always sees two sources of jitter at its input. One is the jitter of the input signal itself, which is what people have in mind when they expect an SRC to solve it. The second is jitter caused by resampling the input clock to its master clock (which may be linked to the output frequency or even a third clock source, in which case the output sampling frequency will be a second source of such errors). The SRC "sees" the input sampling rate only in intervals dictated by its master clock. In most realistic cases this jitter source will actually dominate.
Jitter and PLL modes
The TI SRC4192 has several PLL settings among which it chooses depending on the amount of jitter present on the input. For normally low amounts (anything we'd practically encounter) of jitter, it has a narrow mode where the ratio estimation register is updated only once every few seconds. This means that between updates the conversion factor is held absolutely constant (ie it operates like a synchronous src), and none of the input jitter makes it to the output at all.
If the jitter is too high for the input fifo to hold it (this fifo is rather short because delay was a design criterion), the PLL reverts to a more traditional mode of operation and the chip will indeed encode the input jitter (albeit attenuated) into the output signal as phase modulation of the audio.
I haven't actually measured the CS8421. However, I find graphs like 24b (see data sheet) telling. There are clear side bands around the test signal. This clearly shows leftovers from the quantisation effect described in the preamble.
By its trick of sampling every few (say 4) seconds, the TI chip insures all of these effects are relegated to an area 0.125Hz wide (where they are arguably quite innocuous), whereas the CS8421 has only a lowpass filter and does pass jitter up to significant frequencies. Since this jitter was actually only created by the SRC process itself, you may actually be worse off after SRC than before.
Filtering
Another point of interest is the filtering. The CS8421 shows some minor images in some of the FFT graphs, but on the other hand has pretty much no inband ripple (and hence less pre- and post-echos) than does the SRC4192. It seems someone has heard my (and other people's) pleas for better inband behaviour, which at this level of performance is probably more important than a minor outband spur.
Interpolation
The actual interpolation process appears to be impeccable on both chips, none of them showing any interpolation related spuriae.
Conclusion?
The CS8421 just misses the mark due to the passing of newly created jitter (again something all ASRCs have to contend with, but something which the TI chip addresses elegantly).
The gripe I have with the TI chip is its inband ripple.
Up to you to pick which you think Hz least.
Cheers,
Bruno
Bruno Putzeys :
Bruno,
Where did you get information on the innards of the SRC4192 and CS8421 chip? If what you said about the SRC4192 is true, then what John Siau of Benchmark Media Systems said are bs:
John Siau:
and later in the head-fi thread, in response to someone's question, he said:
You may check out that thread here:
http://www4.head-fi.org/forums/showthread.php?t=78848&page=4&pp=25
Anyway, thanks for enlightening us.
rlim
Bruno,
Where did you get information on the innards of the SRC4192 and CS8421 chip? If what you said about the SRC4192 is true, then what John Siau of Benchmark Media Systems said are bs:
John Siau:
and later in the head-fi thread, in response to someone's question, he said:
You may check out that thread here:
http://www4.head-fi.org/forums/showthread.php?t=78848&page=4&pp=25
Anyway, thanks for enlightening us.
rlim
Looking at the passband graphs may be helpful to make the distinction.
There are different ways of having a certain amount of passband ripple. One is to have an even ripple wiggling constantly all over the band, another is a single excursion near the edges of the band. The difference is quite important in the time domain.
There are different ways of having a certain amount of passband ripple. One is to have an even ripple wiggling constantly all over the band, another is a single excursion near the edges of the band. The difference is quite important in the time domain.
Hello!
Just pulling this old thread up...
We have been using the CS8421 together with the CS8406 as HiRes digital output for a Pioner DV-575, it works really fine.
Now we would need some more for different purposes, but our distributor only wants to sell a packet of IIRC 72 pcs. Does anybody know a source for smaller quantities, preferably in Europe, or is interested in some chips if we decide to order 72 of them?
Regards,
Holger
Just pulling this old thread up...
We have been using the CS8421 together with the CS8406 as HiRes digital output for a Pioner DV-575, it works really fine.
Now we would need some more for different purposes, but our distributor only wants to sell a packet of IIRC 72 pcs. Does anybody know a source for smaller quantities, preferably in Europe, or is interested in some chips if we decide to order 72 of them?
Regards,
Holger
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