processing with High Dynamic Range (3)

This article explores how some different HDR imaging alike techniques can be adopted right into the audio domain.

The early adopters – game developers

In the lately cross-linked article “Finding Your Way With High Dynamic Range Audio In Wwise” some good overview was given on how the HDR concept was already adopted by some game developers over the recent years. Mixing in-game audio has its very own challenge which is about mixing different arbitrary occurring audio events in real-time when the game is actually played. Opposed to that and when we do mix off-line (as in a typical song production) we do have a static output format and don’t have such issues of course.

So it comes as no surprise, that the game developer approach turned out to be a rather automatic/adaptive in-game mixing system which is capable of gating quieter sources depending on the overall volume of the entire audio plus performing some overall compression and limiting. The “off-line mixing audio engineer” can always do better and if a mix is really too difficult, even the arrangement can be fixed by hand during the mixing stage.

There is some further shortcoming and from my point of view that is the too simplistic and reduced translation from “image brightness” into “audio loudness” which might work to some extend but since the audio loudness race has been emerged we already have a clear proof how utterly bad that can sound at the end. At least, there are way more details and effects to be taken into account to perform better concerning dynamic range perception. [Read more…]

processing with High Dynamic Range (2)

This comprehensive and in-depth article about HDR imaging was written by Sven Bontinck, a professional photographer and a hobby-musician.

A matter of perception.

To be able to use HDR in imaging, we must first understand what dynamic range actually means. Sometimes I notice people mistake contrast in pictures with the dynamic range. Those two concepts have some sort of relationship, but are not the same. Let me start by explaining in short how humans receive information with our eyes and ears. This is important because it influences the way we perceive what we see and hear and how we interpret that information.

We all know about the retina in our eyes where we find the light-sensitive sensors, the rods and cones. The cones provide us daytime vision and the perception of colours. The rods allow us to see low-light levels and provide us black-and-white vision. However there is a third kind of photoreceptors, the so-called photosensitive ganglion cells. These cells give our brain information about length-of-day versus length-of-night duration, but also play an important role in the pupillary control. Every sensor need a minimum amount of incitement to be able to react. At the same time all kind of sensors have a maximum amount that they may be exposed to. Above that limit, certain protection mechanisms start interacting to prevent damage occurring to the sensors. [Read more…]

processing with High Dynamic Range (1)

Back in time when I was at university, my very first DSP lectures were actually not about audio but image processing. Due to my interest in photography I followed this amazing and ever evolving domain over time. Later on, High Dynamic Range (HDR) image processing emerged and beside its high impact on digital photography, I immediately started to ask myself how such techniques could be translated into the audio domain. And to be honest, for quite some time I haven’t got a clue.


This image shows a typical problem digital photography still suffers from: The highlights are completely washed out and so the lowlights are turning into black abruptly w/o containing further nuances  – the dynamic range performance is pretty much poor and this is actually not what the human eye would perceive since it features both: a higher dynamic range per se but also a better adoption to different (and maybe difficult) lighting conditions.

On top, we have to expect severe dynamic range limitations in the output entities whether that’s a cheap digital print, a crappy TFT display or the limited JPG file format, just as an example. Analog film and prints does have such problems in principle also but not to that much extend since they typically offer more dynamic resolution and the saturation behavior is rather soft unlike the digital hard clipping. And this is where HDR image processing chimes in.

It typically distinguishes between single- and multi-image processing. Within multi-image processing, a series of Low Dynamic Range (LDR) images are taken in different exposures and combined into one single new image which contains an extended dynamic range (thanks to some clever processing). Afterwards, this version is rendered back into an LDR image by utilizing special  “tone mapping” operators which are performing a sort of dynamic range compression to obtain a better dynamic range impression but now in a LDR file.

Within single-image processing, there must be one single HDR image already available and then just tone mapping is applied. As an example, the picture below takes advantage of single-image processing from a RAW file which typically does have much higher bit-depth (12 or even 14 bit as of todays sensor tech) opposed to JPG (8 bit). As a result a lot of dynamic information can be preserved even if the output file still is just a JPG. As an added sugar, such a processed image also translates way better over a wide variety of different output devices, displays and viewing light conditions.


tasty meal preparations with Density mkIII

Since precise routing and stuff like that is not taken down into the cookbook as of now, here are some exciting tips and tricks to experiment with and maybe to obtain a different approach to cook audio with Density mkIII.


As a starter just use the default preset and dial in huge amounts of compression right with the DRIVE knob. Now mix this back to the dry signal by using the DRY:WET option to obtain a thick sounding result (New York style compression). Since the COLOR option ignores any DRY:WET settings one can dial it in afterwards to thicken the soup even further. Hmm, tasty!

Second course

Set DRY:WET back to a 100% wet signal but also pull RANGE back to the left so that there will be no gain reduction anymore. There is no compression anymore now but one can still use the MAKEUP knob to drive the gain of the non-linear circuits. Use this and experience a hot (driven) meal.

Main course

By finishing the second course, you not only have a sophisticated non-linear amplifier now where you can dial in the coloration with the COLOR knob to taste. You also can use this in M/S mode to adjust the stereo imaging in a quite unique fashion just by adjusting the amounts of saturation per channel right with the MAKEUP knobs. Omph, I’m feelin so wide now!


Just dial in again some amounts of compression by turning RANGE clockwise, maybe full to the right but RELAX the attack times so that some transients can pass. Those will be eaten now by the non-linear amplifier as an added sugar.

Espresso, anyone?

preFIX 1.0 – out now!

preFIX – getting those alignments done

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preFIX – final teaser and release info


preFIX - gate and expander section with detailed sidechain fitering options

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the gate/expander in use

written by susiwong

A basic gate has a single parameter, the threshold – when the level is above the threshold the signal passes unchanged, when the level drops below the threshold the signal gets switched off, simple as that. Attack time ideally should be as fast as possible without causing clicks or distortion, so it’s preset to a sensible compromise with most gates, a few good gates even offer you a choice of two settings. Knee, hold and release determine shape and speed of the fade out, release is responsible for the overall decay time, knee changes the behaviour around the threshold level, helping you avoid the dreaded “motorboating” effect where the gate switches on and off rapidly. Think BSS or Drawmer gate vs Alesis compressor …

Hold simply specifies the “reaction time” from the moment the signal passes the threshold till the begin of the gain reduction – critical to preserve as much meat as possible from drums or keeping guitar decay intact. This is mostly what separates the good from the bad and the ugly. Last is the “range” or “floor” parameter, it sets a certain minimal volume to which the signal gets attenuated when dropping below the threshold, instead of being muted completely. Very helpful when you need to reduce the background noise between a singer’s phrases for example, much less obtrusive than muting the track completely. Set the floor so the background noise gets masked well enough by the music, often 3dB or 6dB are enough. This technique is also known as downward expansion, paired with a longer release and soft knee it’s often used for distorted guitars (with slow decay), too.

Some good gates offer sidechain filters allowing you to “zero in” on the important part of a complex signal, take a tom mic of a multi-miced drumset for example, where a lot of similar signals (bleed) are fighting for control. Difficult even with sidechain, impossible without. Worth noting that these filters do NOT influence your audio signal, only the signal used for detection, hence the name sidechain. And finally an external sidechain allows you to even borrow a signal from another channel to trigger your gate – the creative options are huge.Unfortunately not all hosts have this implemented in a user-friendly way. One popular example is tightening up the bass by triggering its gate from the kick. [Read more…]

loudness wars – episode IV

Yes, a new hope. While some of the recently established  metering systems did not successfully managed the loudness race problems in general there seems to be a new hope concerning those issues and this comes from the broadcasters standardization efforts. Started in 2006 the ITU recommendation BS.1770­‐1 defined already some replacement for the common QPPM metering and instead was oriented towards loudness metering. [Read more…]