Copyright: Copyright (C) 1996-1997 Algorithmix GmbH


Contents
Contents	Algorithmix® DC-Removal Filter PlugIn

Overview	Application Tips

Fig.1: Screenshot of DC-Removal PlugIn window.

Copyright © 1996-1997 Algorithmix GmbH. All rights reserved.

 Help file last modified: December 13, 1997.


Overview
Overview	Algorithmix® DC-Removal Filter PlugIn

Most of today’s multimedia boards are equipped with low-cost analog-to-digital converters that tend to produce a so-called DC drift. This means the analog zero signal is not converted to digital zero, but to a certain positive or negative value called a DC-offset. The left part of Fig. 2 demonstrates signal with a positive DC-offset. All other non-zero samples are also shifted by the amount of the DC-offset. To avoid signal clipping, the input volume has to be decreased compared to an ideal converter, resulting in a narrowed dynamic range of the recorded signal. It is not uncommon for this to measure five bits of DC-offset, corresponding to approximately a 30 dB dynamic range loss! Frequently the converter drift is not constant and varies with time or temperature.

The low-level audio signal including DC-offset, or even a high-level signal attenuated digitally can produce very annoying sounds on the playback side due to asymmetry.

The DC-Removal Filter PlugIn from Algorithmix® is a remedy against those recordings tainted with DC-offset. It removes DC-offset from sample strings, bringing your signal perfectly to the middle of the system’s dynamic range as shown in Fig. 2 on the right.

The DC-Removal Filter is designed as a digital high-resolution (80 bits) highpass filter with a very low cut-off frequency (a few Hz). It allows the removal of DC components from poor recordings even if the value of the DC-offset permanently drifts.

   Fig.2: A signal tainted with DC-offset (left) and after DC-filtering (right).

The presence of the DC-offset can be examined separately for the left and right channels in the display.  The exact peak values of the DC-offset are monitored on the right side of the PlugIn window. These values are permanently updated and hold on the highest level occurring to the current time point. By clicking the reset button, you can reset the numerical peak values any time you want. Thereby, the PlugIn begins to cumulate the new DC-offset peak value.

Copyright © 1996-1997 Algorithmix GmbH. All rights reserved.

Help file last modified: December 13, 1997.


Application Tips
Application Tips	Algorithmix® DC-Removal Filter PlugIn

By using the Algorithmix® DC-Removal PlugIn, you can easily test the drift of the analog-to-digital converter on your soundcard. The best way is to record a steady signal. A sinewave signal is recommended but not absolutely necessary. The recording level of the test signal has to be pretty high, just below any clipping occurs. The amount of the converter drift corresponding to the DC-offset can be read after playing back a few seconds of the test signal through the activated DC-Removal PlugIn . Dividing the peak value monitored in the PlugIn window by  6 [dB/bit] you get the number of bits lost because of the pure converter quality.

It is recommended that you always use the DC-Removal Filter PlugIn as the very first PlugIn in the processing chain to prepare a DC-offset free signal for any other PlugIn. The improvement of the overall sonic quality, especially for low-level signals, can be dramatic.

Due to high-precision design, the DC-Removal Filter PlugIn can be chained into the PlugIn-Station by default without being afraid of any signal degradation even in the case of perfectly recorded sample strings.

For further information about our other PlugIns and new products visit us on the Internet at:

http://www.algorithmix.com

or send e-mail to:

support@algorithmix.com

  - if you need any information about installation and performance of this product.

info@algorithmix.com

  - if you have general suggestions and questions concerning our product line.

Copyright © 1996-1997 Algorithmix GmbH. All rights reserved.

Help file last modified: December 13, 1997.