PCM5102a - Can anyone explain De-Emph and the Filter Options?

[dwjames]

Hi Guys,
I've got an XMOS based USB to I2S board and a DAC board using a PCM5102a on the way to me from DIYINHK and in doing a bit of reading up I notice that there are 2 options with the PCM5102a.
The first is a choice between normal and low latency filter, the other is to enable/disable the De-emphasis control for 44.1kHz sampling rate.

I've had a scan through the datasheet here:
http://www.ti.com/lit/ds/slas859a/slas859a.pdf
But it doesn't explain the effects of the options in a way which I understand and a search on google doesn't bring much enlightenment either..

Can anyone explain in laymans terms what these are, what the likely audible benefits or characteristics are and when they are recommended to be used please?

Realistically, I'll be listening to 44khz CD rips and internet streams from Pandora and such most of the time.

thanks in advance,
James

 

[olev]

There are some old CD's that came with PRE-emphasis - if you listen to them with no audio processing they sound like they have way too much highs. DE-emphasis is used to make the volume of high frequencies lower. Basically it was meant for tape, where you know you are losing high frequencies (or getting high frequency distortion that would cover real signals) so before recording you amplify them, and when playing back just one step before the speakers you de-amplify by the same amount.

But these CD's are now really rare, for example one "famous" one is Pink Floyds Dark Side of the Moon early Japanese Black Triangle CD. If you literally don't have CDs that are in cases with no barcode (the early CDs came out before UPC code was standardized) then you are just muting highs when you turn on de-emphasis.

BTW I just finished my test build for the same hardware. I'm building it in the first case that got me interested in hi-fi DACs - Zero DAC 🙂 With the original transoformer, I had to take off the vinyl covering to get to the center tap of 14V supply and separate the windings (added the green wire) because the diyinhk PSU uses dual positive regulators - can't be used with center tapped transformers.

 

[Ken Newton]

The two filters

...The first is a choice between normal and low latency filter, the other is to enable/disable the De-emphasis control for 44.1kHz sampling rate....But it doesn't explain the effects of the options in a way which I understand and a search on google doesn't bring much enlightenment either...Can anyone explain in laymans terms what these are, what the likely audible benefits or characteristics are and when they are recommended to be used please...

Datasheet pages 15 - 21 rather clearly show the technical effects of the two filters. In terms of their use, the normal linear-phase FIR filter is what would typically be used in CD playback. Some audiophiles, however, feel that such filters contribute to creating a subjectively irritating 'digital sound' quality. The low-latency (meaning, low signal processing pass through time delay) filter is a minimum-phase IIR implementation. It is intended to be used in studio editing applications where low signal processing time delay may be required.

In home listening application, some audiophiles feel that minimum-phase filters generate a less irritating sound quality than do typical linear-phase filters. The good news is that the 'FLT' pin-11 makes it easy to toggle between the two filters, so you can decide which you subjectively prefer.

 

[dwjames]

Excellent. thanks guys for taking the time to explain 🙂
Both the filter and the d-emph are set up to be fairly easy to change on the diyinhk board with dedicated jumper points near the bottom in this pic

But it sounds like it's likely to be best for what I need if I just leave them alone 🙂

That looks nice Olev 🙂 For now, I'm just going to be using USB bus power for mine, but with a USB Isolator inbetween.
Then probably later, I'll get a proper power supply and maybe even a case 🙂

thanks again.
James