DC offset correction in recordings?

[Martini]

Hi all,
I use Audirvana Origin on a Mac for my music library organization and playback. It has a feature called Audio Scan in which you can scan individual tracks and it provides resolution verification and can also note the number of DC offset errors found. Now, I don't know how good a feature this is, but if it is accurate then I've stumbled across some tracks/albums that have issues. Since it is track by track, it would take way too much time to scan my entire library, so what I've found is solely by random sampling.

Questions are:

• Is this a concern?
• Is there way to correct this in post production recordings? I do not see anything in available in Audirvana, nor anything noted in dBPowerAmp.
• And if so, is there a program that can batch check the integrity of a music library? Maybe including inter-sampled overs?

Thanks!

 

[somebodyelse]

Whether it's a concern depends on your playback chain - whether it passes DC all the way to the output, and how it reacts if it encounters DC in the signal. It was recently noted with one of the Topping DAC/headphone amps (DX5 II?) that certain tracks known to have DC offset in the recording would trigger its DC protection. Other components may be AC coupled (so can't pass DC) or have a DC servo to remove offset.

That comes on to the next part - correcting it. Some systems do it inherently. If you need to correct it in the files then you can use a high pass filter, or a DC removal function if your audio editor includes one. I think you can do everything necessary with sox - it's a command line audio processing utility so ideal for use in a batch file.

 

[Martini]

Whether it's a concern depends on your playback chain - whether it passes DC all the way to the output, and how it reacts if it encounters DC in the signal. It was recently noted with one of the Topping DAC/headphone amps (DX5 II?) that certain tracks known to have DC offset in the recording would trigger its DC protection. Other components may be AC coupled (so can't pass DC) or have a DC servo to remove offset.

That comes on to the next part - correcting it. Some systems do it inherently. If you need to correct it in the files then you can use a high pass filter, or a DC removal function if your audio editor includes one. I think you can do everything necessary with sox - it's a command line audio processing utility so ideal for use in a batch file.

Thanks. I'll have Genelec SAM system, stereo monitors & sub. It is fairly new to me, moving from Benchmark electronics to these, so I'm not sure how/if they protect from source based DC.

Music file wise, I may have used the term "post production" improperly. By "post" I meant purchased music, either ripped-CDs or Downloads. So correction would likely need software based, either through resampling with add-in encoder via dBPowerAmp (or other) or through Audirvana. Audirvana does provide some file controls, using SoX or r8brain, but I believe primarily for up/down sampling, which I don't employ.

 

[somebodyelse]

Thanks. I'll have Genelec SAM system, stereo monitors & sub. It is fairly new to me, moving from Benchmark electronics to these, so I'm not sure how/if they protect from source based DC.

In that case the stereo monitors will certainly be high passed to cross with the sub, and the sub is very likely to have a high pass to remove content at lower frequencies than it can handle. The high pass will remove the DC offset.

 

[Martini]

Thanks, good to know. Source-wise I do find it ironic that the majority of albums/track that were indicated to have DC issues were produced by Reference Recordings.

 

[EdW]

Thanks, good to know. Source-wise I do find it ironic that the majority of albums/track that were indicated to have DC issues were produced by Reference Recordings.

Many early digital recordings had dc offsets (mainly mid and late 1980s era recordings). Previously I owned a Topping D90 DAC and I used this to drive the line input of an Arcam integrated amplifier. The amp is ac coupled and I had no issues. Fast forward and I replaced the amplifier with dc coupled Purifi mono blocks driving new KEF blade 2 meta speakers. Several early CD recordings caused dropouts becoming more severe as the volume control on the DAC was increased. No issues with modern recordings though. I wanted ensure that the new speakers were fully protected and that I could enjoy my many older digital recordings.
I also wanted a more versatile DAC and preamp solution with analog input capability. I chose the RME ADI 2/4 pro se which incorporates a 7Hz high pass filter selectable in the software. Problem solved.

 

[Philbo King]

Hi all,
I use Audirvana Origin on a Mac for my music library organization and playback. It has a feature called Audio Scan in which you can scan individual tracks and it provides resolution verification and can also note the number of DC offset errors found. Now, I don't know how good a feature this is, but if it is accurate then I've stumbled across some tracks/albums that have issues. Since it is track by track, it would take way too much time to scan my entire library, so what I've found is solely by random sampling.

Questions are:

• Is this a concern?
• Is there way to correct this in post production recordings? I do not see anything in available in Audirvana, nor anything noted in dBPowerAmp.
• And if so, is there a program that can batch check the integrity of a music library? Maybe including inter-sampled overs?

Thanks!

If DC content is 1% or less it's not really a concern. A lot of brass and bass instruments have DC elements in their waveform naturally (due to harmonic content).

If you're worried about it, add a high pass filter at 10 or 15 Hz.

 

[DVDdoug]

You can't hear DC (zero Hz) but if you have a recording with DC offset you can get a "click" or "tick" at the beginning and end, or if you pause when the DC suddenly kicks-in and kicks-out. If you are hearing these defects you can try removing the offset (with Audacity, etc.). High-pass filtering will take-out the constant DC but it won't fix the click at the beginning.

DC offset usually comes from recording with a "cheap consumer soundcard". It's not common in commercial releases.

It would be rare for the DC to get all the way through to the speakers but the kick-in and kick-out click WILL get through.

DC offset should never be bad-enough to damage the equipment.

Sometimes an asymmetrical waveform (higher positive peaks than negative peaks, or vice-versa) is interpreted as DC offset but some sound waves are naturally like that. True DC offset also shows-up during silence. Depending on the algorithm, "fixing" that may cause a DC offset! And shifting the offset/symmetry could cause clipping.

Maybe including inter-sampled overs?

There is no information between digital samples. Inter-sample overs happen during/after digital-to-analog conversion or when up-sampling. There is software for this that depends in up-sampling but if your DAC has headroom on the analog side, it shouldn't be a problem. Or you can normalize to somewhere around -1dB to create headroom. Of if your setup is using digital volume control, you're rarely hitting 0dB anyway.

Or... It's just not something I worry about. If a recording "sounds bad", lowering the digital volume to prevent inter-sample-overs is unlikely to fix it.

And if so, is there a program that can batch check the integrity of a music library?

No software can tell you if it "sounds good" or "sounds bad". AccurateRip can check the data ripped from the disc. And there are ways of using a checksum to make sure the digital data isn't altered. But usually if the digital data is corrupted it's obvious (from the way it sounds or maybe it "skips" or doesn't play at all, etc.)