Offset waveform after using EQ

[JeffreyD]

I have just applied a 20Hz filter using the EQ effect built in to version x5.3.0. I noticed that my waveform is not offset below the zero line. Is this normal? Does version 5.4 fix this problem?

[admin]

Please explain what you mean by "offset below the zero line".

There has been no change in the EQ code since it was released. So what you have is the same in V5.4.

[JeffreyD]

What I should have said is that in Waveform view the wave forms for both the left & right channels are not centered on the blue line. They are now centered horizontally below the blue line. This can be seen better as I zoom in to expand the waveform and as I increase the view amplitude. If I set a gain fade at the end of the segment, it slopes up to the blue line as the fade occurs.

[admin]

What you describe here is the audio has been recorded with a DC offset which permanently moves the zero crossing up or down by a fixed offset value. EQ will not do this to our knowledge. I expect the source that you recorded from injected this offset and Microsound did not remove it.

How did you record the original file to the hard drive?

1. From a digital audio source using the digital (AES or SPDIF) input ports

2. From an analog audio source using the analog input channels

3. By ripping a tracak from an Audio CD

4. It was stored on a CDROM as a file that you opened and/or copied to the hard drive

This would help me identify the source of your DC offset problem.

BTW: EQ doesn't change a DC offset value.

[JeffreyD]

The original file was recorded through the AES input port from a Tascam DAT machine. The DC offset does not exist on the original file. Only after applying EQ to a segment does it show. The EQ in question was a 20Hz High Band Pass needed to remove noise. I wound up not using the EQ because I was not sure if the CD replication facility would reject the master with such a DC offset.

[clawson]

Actually, Dave, the EQ coding does produce a DC offset with some settings. I reported this as a bug a l-o-n-g time ago but never saw the fix. The problem described here *is* an MTU EQ problem.

Sorry.

Chas.

[admin]

Thanks Chas... guess we missed that one from you.

From what you are saying, there must be a bug in the EQ code. This is not good. EQ is written in DSP Assembly language and is thus very expensive to fix.

Given the length of time EQ has been released, and that Chas and now JeffreyD are the only to report this that I am aware of... but now watch the rest come out of the woodwork , I regret to say this is not of the magnitude to justify repairing.

[geezer]

Chas.-

Although I have never used the EQ much for critical apps except for the lo and hi-pass (where it works "like a real eq" and is very fast and effective), I do occasionally use it for dealing with really odd band-limited source material......Do you have a handle on how you were using the EQ when you noticed the DC offset?...Any recollections?

I don't foresee myself using across-the-board MTU eq for mastering, so I guess this isn't much of an issue unless the hi or lo-pass is inducing DC offset, which I would guess it is not...

[clawson]

Well, Jim, I was looking for my original beta report but
I recently did a lot of hard drive consolidation and purged
a lot of that kind of stuff.

To the best of my recollection, I *was* using a high-pass
filter to try to remove a small DC offset. Ironically, I
wound up inducing a much larger offset instead. At the time,
the symptom was easily repeatable and warranted a bug
report which I sent. I'll have to play around later to
see if I can trigger it again. My schedule is pretty
wacky at the moment so I can't make promises on when.

Stand by...

Chas.