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RME User Forum → DIGICheck → Vector Audio Scope phenomenon
https://www.youtube.com/watch?v=3qqPiA6pt2w
If you playback the above song at 2min 32seconds whilst looking at the vector audio scope you will see a strange phenomenon where the scope moves between the upper and lower x-axis. This is the first time I've seen this happen.
Could someone please explain what causes this?
For reference the same phenomenon occures whilst listening to a copy of the Audio-CD recording.
My vector audio scope settings,
Thank you
I can't explain exactly what's going on, but IMHO, the recording has a high DC component, especially around 2:32 and the last few seconds of the song. I noticed that at 2:32 and the last few seconds of the song, the first 5-6 bits are in red and blue. So I think the problem is in the A/D converter of the interface that the musician is using.
the first 5-6 bits are in red and blue.
What do you mean by this? What is red and blue?
Dimitar wrote:the first 5-6 bits are in red and blue.
What do you mean by this? What is red and blue?
In DigiCheck NG use "Bitstatistics and Noise" tool and you will see what I mean. As far as I know, there shouldn't be any bits colored red while a song is playing.
GolfPutter wrote:Dimitar wrote:the first 5-6 bits are in red and blue.
What do you mean by this? What is red and blue?
In DigiCheck NG use "Bitstatistics and Noise" tool and you will see what I mean. As far as I know, there shouldn't be any bits colored red while a song is playing.
That makes sense, didnt know what you were referencing to.
Separately, while the song is playing, I used Reaper DAW and SPAN plugin (which is free) to monitor simultaneously mid/side components of the signal and in the last 5 seconds in the "mid" component there is a suspicious presence of a harmonic at 100Hz with an abnormally high level. This coincides exactly with the behavior of "Vector Audio Scope" and "Bitstatistics and Noise", which simply reports these anomalies in the signal. It's just that the recording has some technical problems, perhaps caused by the A/D converter.
Apart from the topic. I think if the next version of DigiCheck NG has the same tool as the SPAN plugin, that would be great. SPAN is extremely useful in mixing and mastering, where you can visually monitor whether you are overdoing some spatial effect. For example, whether in a given frequency range the "side" component does constantly exceed the "mid" component, which is not normal.
Dan Worrall has a great video about this plugin and how to use it for mixing, mastering, or just analyzing a finished song (which in this case I did).
https://www.youtube.com/watch?v=iZrWMv02tlA
The red 1 means that this bit does not change for too long, but remains stuck at the value 1.
There is a subsonic disturbance with a period duration between 0.5 and 1 seconds. Not really DC voltage, but almost 4 octaves below the hearing threshold.
The fact that the red 1 appear on the left is due to the binary representation. I will give an example with only 16 bits. 24 and 32 bits are structured the same way, only longer.
Amplitude 0 is binary 0000 0000 0000 0000= decimal 0
The smallest possible positive amplitude 1 is binary 0000 0000 0000 0001 = decimal 1
The largest possible positive amplitude 32767, binary 0111 1111 1111 1111 = decimal 32767
Negative amplitudes begin with a 1 in binary.
The smallest possible negative amplitude -1, binary 1111 1111 1111 1111 = decimal 65535
The largest possible negative amplitude is -32768, binary 1000 0000 0000 0000 = decimal 32768
In the screenshot above, the amplitude between 3 and 3.2 seconds is between 0 and -0,03125
-0.03125 would be 1111 1000 0000 0000.
The first 5 bits would therefore be 1 the whole time, for being between 0 and -1/[2^5].
This applies to all* bit depths, as only the length at the end varies.
(* except 8 bit, because 8 bit is unsigned. Don't ask why, i don't know.)
This is what binary you get, if you look into a WAVE file with an sinus 441 Hz, 0.8 amplitude, sampled signed 16 bit 44.1 kHz.
The amplitude -0.03125 is 64512 in the sinus diagram.
Edit some typos in the text later.
Made a research about 1000 0000 0000 0000. It is a negativ amplitude too.
Thank you rawac! Very interesting and useful information for me
And a happy new year to everyone (in a few hours)! 
Thank you for the very indepth answer rawac. What would have caused this in the first place?
Guys - seriously? We do have a Spectral Analyzer in DC and DC NG, do we?
That YouTube video has low frequency infrasound rumble over its whole runtime. Mastering clearly failed.
Guys - seriously? We do have a Spectral Analyzer in DC and DC NG, do we?
That YouTube video has low frequency infrasound rumble over its whole runtime. Mastering clearly failed.
Just loaded the song up in my DAW and added a high-pass filter and it removed the vector scope anomaly.
Thank you for your knowledge MC.
We do have a Spectral Analyzer in DC and DC NG, do we?
That YouTube video has low frequency infrasound rumble over its whole runtime. Mastering clearly failed.
Matthias I agree with you about the low frequency infrasound rumble. I also first looked at Spectral Analyzer while listening to the song and saw this anomaly in the low frequency, and that's why I wrote in my first post that according to me it's DC, but I always thought it was a result of the A/D converter. I have a lot of music from the 80s and there this "picture" in the sub-low frequencies is quite common.
MC wrote:We do have a Spectral Analyzer in DC and DC NG, do we?
That YouTube video has low frequency infrasound rumble over its whole runtime. Mastering clearly failed.Matthias I agree with you about the low frequency infrasound rumble. I also first looked at Spectral Analyzer while listening to the song and saw this anomaly in the low frequency, and that's why I wrote in my first post that according to me it's DC, but I always thought it was a result of the A/D converter. I have a lot of music from the 80s and there this "picture" in the sub-low frequencies is quite common.
What is other music from the 80s that has the same issue?
I don't mean literally that some other songs look the same in Spectral Analyzer, Vector Audio Scope and Bitstatistics and Noise. I meant that I often observed high readings at 20Hz at a point in the song where there was no reason for it. Readings similar to the screenshots that MC posted.
...
What is other music from the 80s that has the same issue?
One example:
Max Roach – We Insist! Max Roach's Freedom Now Suite
Recorded at Nola Penthouse Studios, New York City, August 31st and September 6th 1960.
Re-released digital on CD Candid Productions Ltd. in 1990
Catalog number CCD79002
AAD transfer in the year 1989 from the vinyl disc! Including crackling too. But very relevant for the history of Jazz and Civil Rights Movement. https://en.wikipedia.org/wiki/We_Insist! Around 60 reissues since 1961. Reissue 2022 from Candid Records (CCD30022) is without DC.
Separately, while the song is playing, I used Reaper DAW and SPAN plugin (which is free) to monitor simultaneously mid/side components of the signal and in the last 5 seconds in the "mid" component there is a suspicious presence of a harmonic at 100Hz with an abnormally high level. This coincides exactly with the behavior of "Vector Audio Scope" and "Bitstatistics and Noise", which simply reports these anomalies in the signal. It's just that the recording has some technical problems, perhaps caused by the A/D converter.
Apart from the topic. I think if the next version of DigiCheck NG has the same tool as the SPAN plugin, that would be great. SPAN is extremely useful in mixing and mastering, where you can visually monitor whether you are overdoing some spatial effect. For example, whether in a given frequency range the "side" component does constantly exceed the "mid" component, which is not normal.
Dan Worrall has a great video about this plugin and how to use it for mixing, mastering, or just analyzing a finished song (which in this case I did).
https://www.youtube.com/watch?v=iZrWMv02tlA
Sorry for OT. Span is great no doubt, was using Span Plus for decades, but switched to TDR Prism when it came out and never looked back. I just find it it much easier to use and much more beautiful to look at. Free too.
https://www.tokyodawn.net/tdr-prism/
These DC-similar effects were quite common in the beginning of the digital conversion era, but vanished when the ADCs improved above 20 bit.
Later recordings in DSD format shows DC again, but typically a fixed value, not modulated.
Thanks to complete working ITB (in the box), software that allows all and anything, plug-ins out of control and clueless operators, DC effects and useless infrasound rumble (inaudible) was back again.
In any case mastering should have removed this low frequency noise. Where this wasn't possible is DSD, at least when the original recording is used unedited and unprocessed. But since years DSD can be recorded with DC levels so low you can't measure them easily (by using ADI-2 Pro and ADI-2/4 Pro [/shameless self-advertising]), so solutions exist even for that.
RME User Forum → DIGICheck → Vector Audio Scope phenomenon
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