Tape Restore Live! for Winamp

Help: Tape Restore Live!: The Bias filter

If a tape sounds dull, the bias correction restores the original frequency response.
If the frequency response of one channel changes over time, Tape Restore Live! can automatically adapt to these changes.

In fact, the bias filter is nothing more than a smart equalizer. Setting it correctly is especially important if the software Dolby B filter is used.

For optimal results (especially if the Dolby B filter is used), the bias settings should be calibated as described in Frequency response calibration. The bias filter contains more settings than the ones that are calibrated this way:

Note: Changing any of these settings might disrupt the Dolby B removing filter.
So, if you are using the software Dolby B filter, make sure that any changes that you make improve the Dolby B playback instead of deteriorating it.

An example where this might be useful is the following: If the volume of one channel drops regularly below that of the other channel, for example when different recordings on a tape were made at different times, and the original recording volume was constant (in other words: The playback of some parts of the tape is better than that of other parts, for one channel), turning on AUTO for that channel to automatically follow the recording characteristics of the other channel would improve the Dolby B playback.

If, on the other hand, one channel was recorded at a lower volume, increasing the volume will disturb the Dolby B filter.

If you are not certain, use the following guidelines:
  • If one channel has a lower volume and sounds duller when played back with the Dolby B filter turned on, it probably needs to be corrected.
  • If one channel has a lower volume and sounds identical (although softer) to the other channel when played back with the Dolby B filter turned on, no correction should be performed.
The Tape bias filter offers the following sliders and settings:

  • master vol left
    master vol right
    These sliders can be used to increase the volume of the left or right channel. Might be useful if one channel is consistently at a lower volume than the other channel.

  • left channel equalizer
    right channel equalizer
    These values should be calibrated. See Frequency response calibration.

    These sliders form an 8-band equalizer for each channel. Use them to increase the volume of frequencies that have decreased in volume due to tape wear etc., and to make the two channels sound equal.

    Make the equalizer for one channel relative to the settings of the equalizer of the other channel. The result is that, for the channel that is relative, the values for each frequency are multiplied with the setting for the other channel.

    In the above image, if RELATIVE TO RIGHT is checked, the 22 kHz band for the left channel would be amplified 2.0 * 1.44 = 2.88 times.

  • AUTO
    When this is turned on for a channel, that channel will automatically follow the sound characteristics of the other channel if this channel drops under the other channel.

    Because that might just be a bit too much, some sliders and settings are offered that limit the adjustment:

    • max rel amp
      The volume of each frequency cannot be amplified more than the value set here.

      Don't set it higher than needed to avoid 'false positives' to be corrected through the roof...

      Usually, if there are problems with a recording, it will mainly affect the high frequencies. Also, the bass sounds are usually mono and recorded at the same volume for both channels.

      Because of this, if the bass level is not equal, it would make sense to assume that one channel was recorded at a lower level, rather than assuming that the recording has deteriorated.

      If AUTO: BIAS ONLY is turned on, Tape Restore Live! uses the bass volume of both channels to limit the automatic adjustment. Only if the high frequencies drop even more than the bass, that part is adjusted.

      When comparing the volumes of each frequency band of both channels, it often occurs that one frequency sticks out. This is often caused by an instrument that is being played on just one channel.

      Turning AUTO: CLUSTERED on lets Tape Restore Live! detect these peaks and remove them.

    The dotted lines (at the bottom of the screen) show how much amplification occurs: The line with very small dots shows what would have been done without the AUTO: BIAS ONLY and AUTO: CLUSTERED filters, the line with larger dots shows the amplification that has actually been performed.

    Based on my own experiences, I have found that the left channel is often in worse condition than the right channel. This has also been confirmed by other people. This is probably caused by the fact that the left channel is on the outside of the tape; the right channel is at the inside.

    Because of that, I always turn on AUTO for the left channel, combined with AUTO: BIAS ONLY and AUTO: CLUSTERED. If I turn any of those two off, the left channel often gets boosted too much, with both limiters on, the correction is nearly perfect (and always better than without correction).
Tape Restore Live! 1.0     (C) Copyright 2006 by Hans van Zutphen     Email: software@hansvanzutphen.com