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

Sokel

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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.
 
OP
M

mike7877

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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
 

AnalogSteph

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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

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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.
 
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mike7877

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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
 
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