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

[Sokel]

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 ?

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:

96Khz I/O


96Khz/352.8Khz I/O

Only DSD reduces it as shown at my other post.

 

[mike7877]

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!

SMSL D400EX DAC Review

Foshan ShuangMuSanLin electronics Co., LTD. founded in 2009 which located in Shenzhen, China. And our branch company VMV Technology(HK) Company Limited registered in HK in 2013. Our company is specialized in the audio DAC, stereo headphone amplifier, power amplifier, and with own R&D...

www.smsl-audio.com

From post in OP:

 

[AnalogSteph]

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).

 

[KSTR]

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.

 

[mike7877]

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

 

[KSTR]

most recordings seem to be normalized to -3dB or lower

More like -0.1dB.

 

[jwmitchell]

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.