Do HDMI cables make a difference for IIS/I2S/I²S-HDMI audiophile DACs?

It's taking a bit longer for my testing of the inexpensive I²S/IIS/I2S-HDMI DDC boxes due to some unexpected results which I'm chasing down currently; hopefully that gets resolved or understood soon.

In the meantime, let me address something that folks might be curious about related to this topic of the I2S-HDMI interface... Does the HDMI cable make a difference to the sound quality?

As with much of audiophilia wherein some members of the culture have the belief that "everything makes a difference", obviously this is not the case and I do not recommend this kind of mindset. There are many things that don't make much, if any difference (as discussed here and here) based on experience and understanding principles of the technology.

Since I have not seen measurements examining the effect of HDMI cables on I²S performance from a DAC, let's do some testing here.

1kHz Test Tone: Does increasing the number of PCM values really matter? And Stereophile's "still listening" to the community (so they say).

Hey there audiophiles, lots happening in life to keep me busy these days as we enter summer 2025, so let's do another little follow-up of a topic based on reader comments.

In the previous post, there was a comment by Mister MB about the 1kHz test tone and the idea that it would be good to use tones that employ more PCM values as quoted from Ken Pohlmann's book Principles of Digital Audio (currently 6th Edition, 2011, from page 81, emphasis mine):

"Digitally generated test tones are often used to measure D/A converters; it is important to choose test frequencies that are not correlated with the sampling frequency. Otherwise, a small sequence of codes might be reproduced over and over, without fully exercising the converter. Depending on the converter’s linearity at those particular codes, the output distortion might measure better, or worse, than typical performance. For example, when replaying a 1-second, 1-kHz, 0-dBFS sine wave sampled at 44.1 kHz, only 441 different codes would be used over the 44,100 points. A 0-dBFS sine wave at 997 Hz would use 20,542 codes, giving a much better representation of converter performance. Standard test tones have been selected to avoid this anomaly. For example, some standard test frequencies are: 17, 31, 61, 127, 251, 499, 997, 1999, 4001, 7993, 10,007, 12,503, 16,001, 17,989, and 19,997 Hz."

Certainly a good point to think about. However, if we look at actual hi-res DACs these days, and the way we're running 1kHz tests to show routinely >100dB SINAD, would we actually see significantly different results depending on how we create these test tones, specifically whether more or less PCM codes are being used in the signal sent to the DAC?

Well, while I still have the Topping DX9 on my testbench, let's have a look at the analog output from the device with a few ~1kHz test tone variants.

Follow-up: Topping DX9 DAC tests. And reduction in the ability to comment on the Stereophile website.

Topping DX9 DAC sitting on Linn Klimax DS/2 which we'll talk about another time.

Hey guys and gals, thanks for the comments and feedback over the years on this blog. It really helps to refine the testing and of course explore broader ideas about audiophilia and what it is we're after in this hobby. I think it's important that we're free to discuss and critique not just the hardware, but also the ideas (including the philosophy and psychology) that "we" as individuals believe in. There's so much unsubstantiated audiophile cultural beliefs out there based on myths such that everything should be up for examination regardless of who says what. It's not unusual to find that audiophile review "high priests" are wrong, and some "heroes" of the audiophile world are nothing more than false prophets.

It's also good to get feedback suggestions on the published measurements, for example in the recent series on the Topping DX9 flagship DAC (based on rare AKM AK4499EQ chip), Nick in the Part III comments suggested that I consider this:

"Hi Archi,

Prior to version 5.40.78 beta rew had a gross error in IMD vs Level plotting, the results were underestimated by about 12 dB. It looks like the version you used has this error.

IMHO there are not enough performance measurements at high frequencies for a complete picture. If still available, it would be very interesting to see THD (without noise) vs frequency performance, accurate THD measurement at 10kHz and wideband fft (without weighting) with a weak signal such as the signal for the DR test.

Thanks!"

Excellent feedback and suggestions Nick, let's focus on checking this out in this post!

Part III: Topping DX9 "15th Anniversary" Limited Edition DAC & Headphone Amplifier - DSD, S/PDIF inputs, headphone out, pre-out, and AMPT. And the desire beyond Perceptibly Perfect.

With Raspberry Pi 'Touch' streamer showing album art running RoPieee, and the Topping DX9 VU meters playing, this looks quite nice in the audio rack!

Let's finish up with the last installment of the review/measurements for the Topping DX9 "15th Anniversary" DAC (see Part I, and Part II previously). As we have seen up to this point, it's quite a unique looking DAC and the initial PCM measurements over USB2.0 look great as a modern hi-resolution converter. In Part II I noted that there was an issue with the 176.4/192kHz frequency response that Topping was able to correct quickly with a firmware update. I'll be using the latest firmware 1.23 for the measurements here.

Let's continue then to dive in and explore the objective performance with some of the other main features for this DAC.

Part II: Topping DX9 "15th Anniversary" Limited Edition DAC & Headphone Amplifier - PCM Filters, Frequency Response & DAC Resolution. (And Trump's ongoing oblivious narcissistic tariff buffoonery.) [Firmware 1.23 Update]

Continuing with the discussion in Part I, let's proceed with Part II of our look at the Topping DX9 "15th Anniversary" DAC as we wade into some of the technical capabilities and performance of this device.

As I discussed the other week, my belief is that for relatively "simple" devices like DACs where what we want is as-accurate-as-possible conversion of the audio data into the analog voltages, measurements are really all we need to characterize the accuracy, the transparency of the device using modern tests and instruments that are capable of capturing details beyond the ability of human hearing. The capability for any device to achieve transparency of course does not guarantee that we'll be able to enjoy the sound or the music which are determined by individual subjective psychological factors.

With that, let's jump into some PCM measurements of this Topping flagship product.

Part I: Topping DX9 "15th Anniversary" Limited Edition DAC & Headphone Amplifier - build, features, listening impressions & subjective luxury.

As many audiophiles will remember, the well-known DAC chip maker Asahi Kasei Microdevices (AKM) suffered a massive fire at their factory back on October 20, 2020 in Miyazaki Prefecture, Japan. This resulted in a shortage of their chips for awhile until they rebuilt the plant and started offering devices again by the end of 2021.

In June 2021, AKM issued a "last time buy" notification for final stock of a number of their products. This included their top-of-the-line DAC chip, the AKM AK4499EQ which was initially released in January 2019 and had made its way into a number of devices over the ensuing couple of years. By later 2021, some devices like the HiFi Rose RS150 had to transition to ESS. With 4 channels, a published THD+N of -124dB (mono mode), 137dB SNR in stereo (140dB mono), DSD "direct" (volume bypass), this chip remains a formidable converter even in 2025 with newer generations of AKM and ESS chip DACs. While audiophiles and manufacturers like to talk about discreet DACs like R2R stuff or custom "Ring" DACs, or DSD-processing DACs (like Meitner products or Playback Designs), while I'm sure they sound great, there is no evidence that these are capable of achieving better objective resolution than state-of-the-art converter chips from semiconductor companies with significant R&D resources.

For comparison, based on company specs, the current premium DAC chips are ESS's ES9039PRO rated at -122dB THD+N mono, and 140dB SNR mono. And AKM's current flagship, the 2-channel AK4499EX DAC released in 2021 listed as THD+N -124dB and SNR 135dB stereo (138dB mono). The AK4499EQ as a 4-channel DAC is a much more complicated chip than 2 AK4499EX's because it also incorporates the sigma-delta modulator internally while the AK4499EX needs to be fed 7-bit modulator data at 5.64/11.29MHz from a separate source like the AK4191EQ ΔΣ Modulator!

So, basically, as a single chip, the discontinued AK4499EQ after only about 1.5 years in production, remains the highest performing device among its peers after all these years; on paper at least.

And that's why I bought one of these for my system - the Topping DX9 "15th Anniversary" Limited Edition DAC & headphone amplifier (US$1299, CAD$1900, depending on tariffs you might do better ordering from China through AliExpress):

This is Topping's flagship DAC, released in late 2023. It's said to be limited edition due to the restricted number of DAC chips; I connected with Topping and was told in total they made about 1800 units.

I bought this unit from the usual retail channels and have no affiliation with the company.