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ESS IMD hump with AKM DAC? (specifically AK4499EXEQ in Topping E70 Velvet)

Well ESS sum 1-bit DACs. Maybe something related here.

@Sokel can you followup your PCM96k vs DSD256 with one more comparison

If you upsample to PCM353kHz you will by-pass ESS first stage oversampling - does that help IMD hump ?



3220d93725d0ffd99ed4ceaa13be6d0a90b72c8e_2_690x374.jpeg
That's just their nomenclature for the final 6 or 7-bit thermometer-coded final DAC.


In my experiments the ESS hump phenomen was completely unaffected by sample rate... that was for an asynchronous implementation of ES9038q2m, running on a fixed 100MHz clock for the final DAC. With a synchronous setup of the chip it might be different but I doubt that.
Yep,same mess:
96000.PNG
96Khz I/O

352800.PNG
96Khz/352.8Khz I/O

Only DSD reduces it as shown at my other post.
 
Looks like Amir's review of the SMSL D400 made it on their website (which I randomly encountered while browsing stores that sell audio stuff)! Lol

And what did I see?! This same IMD hump... How strange!
Both start at -25 and finish at -5

Just thought I'd add it here!


1713373470350.png



From post in OP:
1713373689385.png
 
There has been some speculation indicating that this AKM "ESS hump" may not manifest in the same way (i.e. increased distortion) but rather consist of an elevated noise floor instead... still not ideal but less troublesome. Are there any indications that this may be the case? The spray of harmonics near 0 dBFS is not too promising...

Mind you, at the magnitude we're seeing here (-96 to -99 dBr) it's not at all an issue for audio, I'd be more concerned for non-audio DSP applications (SDR and whatnot).
 
There has been some speculation indicating that this AKM "ESS hump" may not manifest in the same way (i.e. increased distortion) but rather consist of an elevated noise floor instead... still not ideal but less troublesome. Are there any indications that this may be the case? The spray of harmonics near 0 dBFS is not too promising...
The only proper way to find out is looking at individual spectra, vs. frequency and notably vs. level. Better yet, look at the time-domain residuals.
All those THD+N or IMD+N vs level graphs are quite useless in practice and it's a pity that they are still used, for historical reasons mostly.
 
There has been some speculation indicating that this AKM "ESS hump" may not manifest in the same way (i.e. increased distortion) but rather consist of an elevated noise floor instead... still not ideal but less troublesome. Are there any indications that this may be the case? The spray of harmonics near 0 dBFS is not too promising...

Mind you, at the magnitude we're seeing here (-96 to -99 dBr) it's not at all an issue for audio, I'd be more concerned for non-audio DSP applications (SDR and whatnot).
Ah, I didn't know this. Good to know!

Something else to consider, most recordings seem to be normalized to -3dB or lower, and those are pop songs. Most high fidelity recordings will probably only have a transient or two between -3 and 0dBfs, so any extra distortion there will probably be masked by the much increased level
 
Before I start talking, here is l7audiolab's IMD chart for Topping's E70 Velvet, which uses the AK4499EXEQ chipset ((((AK4499EXEQ is post-fire AKM 4499 - it is two chips now, called: AK4499EX and AK4191EQ. Digital processing (ie. oversampling and other optimizations) is done in the 4191, and digital to analog conversion and nothing else at all (no, nothing) is done in the 4499. Separation why? Mainly to reduce noise from interference from proximity of different circuit types)))

View attachment 355722

For comparison, below is l7audiolab's standard E70 performing the same test (E70 uses ESS's ES9028PRO). I used l7audiolab instead of Amir's to have both charts from the same place.
View attachment 355731

The ES9028PRO version of the E70 seems to have a tiny bit of ESS IMD hump in the -32dB to -23dB range, which disappears completely by -20dB, followed by the common and non-problematic slowly increasing distortion from -18dB to -8dB, levelling between -8dB and 0dB, at -112dB. We'd probably see the same, slow, increase in distortion on the E70 Velvet if its IMD hump didn't so drastically affect the shape of the line.

The IMD hump of the AKM chip seems to rear its head at higher level than the [typical] ESS IMD hump. The E70's ES9028PRO's little baby bump of an IMD hump is in the usual position, maybe 2-3dB lower than usual. I think the top half of the E70's ESS IMD hump was completely flattened, and the bottom half remains, so it just looks lower than usual. Anyway... this isn't about the E70, it's about the E70 Velvet, and its IMD hump!

So the E70 Velvet's hump is much more defined than we're used to seeing from ESS.

OK, that's all I have to say on the issue! Lol, I've observed it, and that's all I know!

Oh, I do know one other thing - Techpowerup, they reviewed both the E70 and E70 Velvet. In the process, they opened them both up. They didn't fully disassemble them because there were some difficult to access ribbon cables which connected stuff to the front panel, but they pulled out the boards as far as they could and looked. They said the internals were essentially the same between the devices, except for the DAC part. edit: oh, and ver. Velvet has a slightly upgraded power supply for one of its parts. Not a huge deal.

I think it's great that there are two DACs sharing the same platform - it gives a good opportunity for analysis!

So what's everyone's thoughts? I think this is a really rare find - is it not as rare as I seem to think it is?


To add: irrelevant but I'm curious if anyone knows: have non delta-sigma DACs been observed humping IMD like ESS?
This is very interesting especially as it would seem to belie the title velvet in the AKM version.
 
So perhaps this is why I enjoy the sound on my amazing Fiio M23 DAP/pocketwarmer (with akm4499ex) better with "all to DSD mode" .... Although w/ DSD upsampling, it then gets even warmer, which is perfectly Ok in winter, but not so good in summer. (Never ran out of battery, though, in any listening session but it does bring new meaning to "hot pocket" in summer).

There's something about the fanaticism of using a power-hungry desktop dac in a portable setup that I really enjoy. IMHO the akm4499ex is phenomenal! :)
 
People hi !

TOPPING E70 (ESS) filters ->

F1 (FAST ROLL-OFF & LINEAR PHASE)

F1 (FAST ROLL-OFF & LINEAR PHASE).jpg


F2 (SLOW ROLL-OFF & LINEAR PHASE)

F2 (SLOW ROLL-OFF & LINEAR PHASE).jpg


F3 (FAST ROLL-OFF & MINIMUM PHASE)

F3 (FAST ROLL-OFF & MINIMUM PHASE).jpg


F4 (SLOW ROLL-OFF & MINIMUM PHASE)

F4 (SLOW ROLL-OFF & MINIMUM PHASE).jpg


F5 (FAST ROLL-OFF 'APODIZING')

F5 (FAST ROLL-OFF 'APODIZING').jpg


F6 (FAST ROLL-OFF CORRECTED & MINIMUM PHASE)

F6 (FAST ROLL-OFF CORRECTED & MINIMUM PHASE).jpg


F7 (BRICKWALL)

F7 (BRICKWALL).jpg




TOPPING E70 VELVET (AKM) filters ->

F1 (SHARP ROLL-OFF)

F1 (SHARP ROLL-OFF).jpg


F2 (SLOW ROLL-OFF)

F2 (SLOW ROLL-OFF).jpg


F3 (SHARP ROLL-OFF & SHORT DELAY)

F3 (SHARP ROLL-OFF & SHORT DELAY).jpg


F4 (SLOW ROLL-OFF & SHORT DELAY)

F4 (SLOW ROLL-OFF & SHORT DELAY).jpg


F5 (SUPER SLOW ROLL-OFF = NON OVER SAMPLING)

F5 (SUPER SLOW ROLL-OFF = NON OVER SAMPLING).jpg


F6 (LOW DISPERSION & SHORT DELAY)

F6 (LOW DISPERSION & SHORT DELAY).jpg


In my opinion, the best filters to use with this DACs are:

- for the E70 (ESS) -> number 'F1'

- for the E70 VELVET (AKM) -> number 'F3'

Regarding the filters proposed for the TOPPING E70 VELVET (AKM version), it should be noted that the rejection noise at the NYQUIST frequency is not measurable for the selections with 'SHARP ROLL-OFF' :cool:
 
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OK, understood.
Anyway, the issue is there with almost any DAC chip, to different amounts of course.
Now we know the reason why datasheets seldom show close-up filter responses :
View attachment 355960
ESS allows for custom FIR filters so maybe the E70 ESS version is using that...
ESS specify the pass band ripple in the datasheet for many of their DAC chips. For the 9028 Pro, this is on page 48 of v3.7. Topping's filter 5 is Fast Roll-Off Apodizing, per the manual, i.e. the third filter in the datasheet which has notably high pass band ripple at +-0.075 dB.
Screenshot 2025-02-05 at 17.37.35.png
 
ESS specify the pass band ripple in the datasheet for many of their DAC chips. For the 9028 Pro, this is on page 48 of v3.7. Topping's filter 5 is Fast Roll-Off Apodizing, per the manual, i.e. the third filter in the datasheet which has notably high pass band ripple at +-0.075 dB.
View attachment 426250
So which filter would you recommend?
 
Personally i said the filter 1, this can be seen on TI's DATASHEETS: Pass band Ripple and bandwidth = +/- 0.002% and Stop band = < -120dB (25.1 kHz band rejection image called 'NYQUIST frequency').

In addition, the signal level only decreases from 22kHz, which is higher than the so-called 'Hi-Fi' band, which is set at 20kHz in the higher frequencies.

JIW is also right for the E70 VELVET ;)
 
Personally i said the filter 1, this can be seen on TI's DATASHEETS: Pass band Ripple and bandwidth = +/- 0.002% and Stop band = < -120dB (25.1 kHz band rejection image called 'NYQUIST frequency').

In addition, the signal level only decreases from 22kHz, which is higher than the so-called 'Hi-Fi' band, which is set at 20kHz in the higher frequencies.

JIW is also right for the E70 VELVET ;)

I should have specified Velvet lol. Thank you!
 
To minimise pre- and post-echoes? Fast Roll Off, Linear Phase (E70 F-1) and Fast Roll Off, Minimum Phase (E70 F-3).

Do you concur (post 53)?
 
Of course not mike7877 but the posts have progressed so much since then, sorry ;)
 
I should have specified Velvet lol. Thank you!
Use the sharp roll off filters. Short delay is minimum phase. They have the same pass band ripple of +-0.005 dB according to the AK4499 data sheet.
 
TOPPING E70 VELVET (AKM) is better than the TOPPING E70 (ESS) according to my personal 'blind' listening experience using a friend who switched these two DACs without me knowing which one was playing (the maximum output levels had been set to the same voltage).

I know that listening tests are purely subjective and I know very well the (objective) measurements made on these two DACS but the fact remains that there are sound differences between these two DACs although I don't know why... :confused:
 
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