This is a review and detailed measurements of a generic USB to balanced AES digital converter sold on Aliexpress. It was kindly drop shipped by a member and costs US $17.02.
The converter is everything you want it to be: simple with a robust aluminum case and even included USB cables! Member interest is in using such converters with professional studio monitors that only have AES input. Let's see if it can transfer digital bits from USB to AES including timing without spoilage.
Aliexpress USB to AES Converter Measurements
Let's start with purely digital test case. USB signal from Windows computer to digital AES input of the Audio Precision analyzer, and examining the jitter spectrum:
The lines in green (barely visible) are the spectrum of jitter when I am using Audio Precision's own AES output, going to its input using a 6 foot XLR cable. Red replaces the source with the USB to AES converter. As you see, we take a massive hit to the tune of 50 dB. Clearly there is some kind of clocking issue here.
Serial interface on DACs has some amount of filtering (of high frequency) jitter. Let's see if they can handle this amount of degradation. I powered on my D70s which is on my desk, first using Audio Precision as the AES input:
We see the squeaky clean response of the DAC as we expect. Now let's feed its AES input through the generic USB to AES converter:
Wow, that is some serious damage! FYI I switched to 48 kHz and problem remained.
Conclusions
It is clear that these converters have a serious design problem when it comes to conveying the digital signal and its timing. They may be using simple USB adaptive interface and with it, carry all the computer USB jitter. Or some other problem. It is a serious shame as the cost is more than reasonable. Seeing how the analog output of the DAC is disturbed by large factor, it is hard to justify using it. Note that some AES receivers may even fail to lock into a signal this bad.
So yeah, "bits are not always bits." See my video on this (around 9 minute mark):
I can't recommend the Aliexpress generic USB to AES Converter. Hopefully we can find a bargain one that works well in the future.
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As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The converter is everything you want it to be: simple with a robust aluminum case and even included USB cables! Member interest is in using such converters with professional studio monitors that only have AES input. Let's see if it can transfer digital bits from USB to AES including timing without spoilage.
Aliexpress USB to AES Converter Measurements
Let's start with purely digital test case. USB signal from Windows computer to digital AES input of the Audio Precision analyzer, and examining the jitter spectrum:
The lines in green (barely visible) are the spectrum of jitter when I am using Audio Precision's own AES output, going to its input using a 6 foot XLR cable. Red replaces the source with the USB to AES converter. As you see, we take a massive hit to the tune of 50 dB. Clearly there is some kind of clocking issue here.
Serial interface on DACs has some amount of filtering (of high frequency) jitter. Let's see if they can handle this amount of degradation. I powered on my D70s which is on my desk, first using Audio Precision as the AES input:
We see the squeaky clean response of the DAC as we expect. Now let's feed its AES input through the generic USB to AES converter:
Wow, that is some serious damage! FYI I switched to 48 kHz and problem remained.
Conclusions
It is clear that these converters have a serious design problem when it comes to conveying the digital signal and its timing. They may be using simple USB adaptive interface and with it, carry all the computer USB jitter. Or some other problem. It is a serious shame as the cost is more than reasonable. Seeing how the analog output of the DAC is disturbed by large factor, it is hard to justify using it. Note that some AES receivers may even fail to lock into a signal this bad.
So yeah, "bits are not always bits." See my video on this (around 9 minute mark):
------------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/