2010
07.25

An overview of my work of transforming the DSPXmini-FM processor to the DSPXmini-FM SE (Second Edition).

DSPXmini-FM SEDSPXmini-FM SE processor

Anybody who has some experience in processing, knows it’s VERY subjective. People hear differently, are sensitive to different things, prefer different “flavors” and textures of the sound, etc. Describing processing and the sound becomes quite difficult as well. Nevertheless, using some short audio clips I’m going to attempt to illustrate the sound and the thought process behind re-designing the original DSPXmini processor. As they are only short clips, an untrained ear may not perceive as significant difference as you would, had you had an opportunity to listen to these processors and effects for longer time. Keep that in mind while listening.

As with all re-designs, things usually start with the discontent of some aspects of the existing product and an idea that things could be done better… Having spent enough hours carefully listening to the processor, you get to know its character (almost like you would a person). You get to the point where you can anticipate how it will behave in certain situations, what reaction you will you get for certain input. You get to know its good sides and its flaws. And if these flaws are obvious, displayed too frequently and cannot be tamed down sufficiently with available parameters adjustments, this is where a designer starts to consider if things can me improved.

The original DSPXmini had several things that needed to be improved in my opinion. Let me try to illustrate them to you:

Note: It’s best to use headphones (or a hi-fi system) to listen to these clips. The processor was set to 50µs pre-emphasis and the ‘AC’ preset.

  1. The overall frequency balance that the processor always tried to created was too bright. Inherently in the design of the processor, there was a strong tendency to shift emphasis to high frequencies. To the point of the sound becoming too silky and strident:

    Note: After you press play, it may take some time for video to load.

    [flowplayer src=’http://www.gorantomas.com/wp-content/uploads/2010/07/FreqBal1.mp4′ width=368 height=272 splash=‘wp-content/uploads/2010/07/vs.jpg’]
    [flowplayer src=’http://www.gorantomas.com/wp-content/uploads/2010/07/FreqBal2.mp4′ width=368 height=272 splash=‘wp-content/uploads/2010/07/vs.jpg’]

  2. There was an irritating “hole-punching” effect in the high-frequencies, where the processor would distort and duck the high-end on HF transients such as the words starting with an ‘s’ and other sibilants:
    [flowplayer src=’http://www.gorantomas.com/wp-content/uploads/2010/07/HolePunching.mp4′ width=368 height=272 splash=‘wp-content/uploads/2010/07/vs.jpg’]

  3. The overall sound was too busy, too mashed in. More often than not, you could hear the layer of processing rather than being able to listen to the music and enjoy it. Additionally, the processor was breathing too much, slowly changing the sound and the frequency balance unnaturally during the song:
    [flowplayer src=’http://www.gorantomas.com/wp-content/uploads/2010/07/Unstable.mp4′ width=368 height=272 splash=‘wp-content/uploads/2010/07/vs.jpg’]

  4. The low-end texture was too tight and constrained, rather than being open, big and adding power to the sound.

By listening to the processor, observing the meters and noticing what effect the adjustments of the parameters had on the sound, it was obvious to me that the major source of the problems of ducking, changing frequency balance and busy and constrained sound was with the 4-band limiter. After looking at the algorithm structure and trying to modify it to correct these problems, it became clear that a completely different approach was needed. This was when I embarked on the development of the limiter algorithm from the scratch. Most of these ideas came from my home-brew processing experiments in analog. I also wasn’t going to satisfy on the first idea I had, but on the one that sounded the best. That took time, but in the end, the new limiter algorithm with smart program-dependent attack, release and gating circuits and a few tricks to handle the pre-emphasis more naturally, was born.

ToDo listSneak peak on the excerpt from my ToDo list during development

However it did not solve all the problems. Mainly, there was still a lack of bass punch. And in my book, a solid, powerful low-end is the foundation of a good sound on-air! I felt the new limiter could handle much more than it was being taxed with, so I ended up making tweaks to the AGC in order to change the energy balance handled by the AGC vs the limiter. This produced some results, but still not enough, so another major re-design was in order – the crossover. Without going into the complexities of crossovers, the new design really helped the limiter bring out some of the bass thump and low-end up in the overall sound. Finally, a distortion-controlled clipper received some tweaks in order to reduce the aliasing distortion and the transformation was finished with several more weeks of tweaking and fine-tuning of all the processing stages so that they would work synergistically and smoothly with each other.

And here are the results (a sort of before and after comparison):

Note: It’s best to use headphones (or a hi-fi system) to listen to these clips. Both processor were recorded in the same environment, with the same input and output settings, 50µs pre-emphasis and running the ‘AC’ preset.

  1. Frequency balance:
    [flowplayer src=’http://www.gorantomas.com/wp-content/uploads/2010/07/VS-FreqBal.mp4′ width=368 height=272 splash=‘wp-content/uploads/2010/07/vs.jpg’]
  2. Stability of the sound:
    [flowplayer src=’http://www.gorantomas.com/wp-content/uploads/2010/07/VS-HolePunching.mp4′ width=368 height=272 splash=‘wp-content/uploads/2010/07/vs.jpg’]

  3. Low end texture and bass thump:
    [flowplayer src=’http://www.gorantomas.com/wp-content/uploads/2010/07/VS-LowEnd.mp4′ width=368 height=272 splash=‘wp-content/uploads/2010/07/vs.jpg’]

For better comparison, here are two longer clips with mixed music of both the original DSPXmini-FM and the DSPXmini-FM SE:

Note: You can switch between the clips by pressing the Play buttons (only one clip will play at a time). You can also position the playback bar where you want it to start playing so you can easily compare processors at different parts of the music mix. These players will play 128 kbps MP3 encoded audio, but you can download the original WAV files by clicking on the Download (down arrow) buttons.


Source audio


Original DSPXmini-FM (AC preset)


DSPXmini-FM SE (AC preset)

The mini SE is not without flaws… One thing that I wanted to do is tackle the AGC which could be better and more effective, and the overall cleanliness could be improved as the processor will not exactly “burn the dial” with loudness and punch… Personally, I always want to improve more and I’m rarely completely satisfied with something. But then you have to consider the fact that this processor costs only EUR 1200/USD 1500 (at the moment of this writing) and there’s only so much development a company can and wants to afford, with a profit from the sales at that price point.

However, I believe the mini SE really matured from the original processor and improved on most of its previous weaknesses. Aside from comparing the processor with its competitors, the way I judge whether the processor is good, is to see if I can listen and forget about the processor and just enjoy the music… Whatever the processor does it has to be natural, in harmony with the audio and it must not detract my attention by getting in the way and doing something unnatural. And I believe I was able to get very close to that important goal with the DSPXmini-FM SE.

The DSPXmini-FM SE was presented at the IBC 2008.
Visitors could compare it to the original DSPXmini-FM and other processors.

There was quite a bit of skepticism about what will come out of my design. But in the end, pretty much everybody liked the improvements and the new sound of what became the Second Edition of the DSPXmini-FM and the reactions from the customers proved it as well.

Goran Tomas

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