Atlona HD570 distortion / subsonic transients

In my linux pc-based dsp system for crossover and EQ of active loudspeakers, I use a pc to send 6 channels of processed audio over hdmi, with an Atlona AT-HD570 to convert all channels to analog before amplification.  Recently I discovered that this setup can distort badly at moderately high signal levels, in a way that produces large transient subsonic signals which, when amplified, could permanently damage loudspeaker drivers.  My measurements point to a flaw in the HD570.
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Asymmetric Clipping = Over-Excursion

I want to use my LX521 loudspeakers to amplify live instruments (especially digital piano) but have run into a problem.  The piano has high dynamic range, with attack transients that take up lots of headroom.  While the ATI6012 amplifier can achieve high sound levels on studio-mastered material, it can’t keep up with the transients in the sample library on my piano.  Achieving realistic sound levels means pushing the amplifier into clipping.

But because the piano’s attack transient has an asymmetrical waveform, when the amp clips it does so asymmetrically.  This generates a DC signal that pushes the driver into over-excursion.  Although some clipping distortion might be acceptable on its own, over-excursion makes some truly objectionable noise.

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Phase Issues with Digital Pianos (part 2)

Following up on an earlier post, I’ve been investigating why digital pianos sound so bad in stereo.  I did a spectral analysis on the outputs of my Yamaha CP50 stage piano.  The results confirm what I and others have been hearing: because of how they are sampled, stereo pianos don’t reproduce well except in headphones.

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Phase Issues With Stereo Digital Pianos

Musicians often complain that their digital piano sounds good through headphones but terrible through an amp/PA, describing their live piano sound as “thin”, “nasal” or “boxy”.  This can be frustrating and musically uninspiring.  Because the piano sounds good through ‘phones, people naturally blame their amp/speakers and seek a solution there.

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rt-plugins-0.0.4 released

I just posted version 0.0.4 of my LADSPA plugins for doing crossover/equalization of active loudspeakers.  Just a couple of changes to note:

  • First-order low- and high-pass filters are now available.
  • The build system has been moved to cmake; hopefully this makes it easier to build the plugins on other platforms.  Also some code cleanup and restructuring. (All thanks to Florian Franzmann.)

There’s no need to upgrade if these changes don’t affect you.

At some point the LADSPA API will become deprecated and my plugins will have to be migrated to LV2.  Any volunteers?