What loudspeakers and audio transformers do have in common

Or: WTF is “group delay”?

Imagine a group of people visiting an exhibition having a guided tour. One might expect that the group reaches the exhibitions exit as a whole but in reality there might be a part of that group just lagging behind a little bit actually (e.g. just taking their time).

Speaking in terms of frequency response within audio systems now, this sort of delay is refered to as “group delay”, measured in seconds. And if parts of the frequency range do not reach a listeners ear within the very same time this group delay is being refered to as not being constant anymore.

A flat frequency response does not tell anything about this phenomena and group delay must always be measured separately. Just for reference, delays above 1-4ms (depending on the actual frequency) can actually be perceived by human hearing.

This always turned out to be a real issue in loudspeaker design in general because certain audio events can not perceived as a single event in time anymore but are spread across a certain window of time. The root cause for this anomaly typically lies in electrical components like frequency splitters, amplifiers or filter circuits in general but also physical loudspeaker construction patterns like bass reflex ports or transmission line designs.

Especially the latter ones actually do change the group delay for the lower frequency department very prominently which can be seen as a design flaw but on the other hand lots of hifi enthusiast actually do like this low end behaviour which is able to deliver a very round and full bass experience even within a quite small speaker design. In such cases, one can measure more than 20ms group delay within the frequency content below 100Hz and I’ve seen plots from real designs featuring 70ms at 40Hz which is huge.

Such speaker designs should be avoided in mixing or mastering situation where precision and accuracy is required. It’s also one of the reasons why we can still find single driver speaker designs as primary or additional monitoring options in the studios around the world. They have a constant group delay by design and do not mess around with some frequency parts while just leaving some others intact.

As mentioned before, also several analog circuit designs are able to distort the constant group delay and we can see very typical low end group delay shifts within audio transformer coupled circuit designs. Interestingly, even mastering engineers are utilizing such devices – whether to be found in a compressor, EQ or tape machine – in their analog mastering chain.

tips&tricks with SlickEQ

Note: Some of the tips rely on features from the GE version.

Mixing against HP/LP combo

A good generic practice when EQing several tracks in a mix is too start by dialing in HP/LP combinations by an  appropriate level and then do further EQing/mixing against those settings. Also using the tilt filter is a good idea to apply very first and rough tonal corrections and then working out the details afterwards with the three EQs.

Preserving low-end energy when high-pass filtering

A cool trick to preserve some low-end energy when high-pass filtering is applied is to boost the low-end while using the EQ-SAT feature. As you can see in the routing diagram the HPF comes after the main EQs and EQ-SAT. This way, harmonic overtones are generated based on the fundamentals before the HPF is applied.

Decoupling the low-end

The low-end EQ features a “Phi” option switch which allows to decouple the low-end by an allpass filter network. The crossover can be freely adjusted with the normal frequency control in this band while the gain control does not have any effect in this mode. This may work great for that mellow bass drums just as an example but in other cases it might loose some definition as a trade-off.

Compare different settings

SlickEQ contains two effect settings slots, A and B. Use them in combination with the automatic output gain control to AB test different settings. Within the plugin you can move settings between A and B but also copy&paste is there to freely copy settings between different plug-in instances. Also, undo/redo comes in handy here.

Adjusting precise values

The gain/frequency displays can also be used to enter specific values and also shortcuts are accepted, e.g. “5k” can be entered to set a value to 5000. And did you know that SlickEQ has mouse-wheel support?

 

 

preFIX 1.0 – out now!

preFIX – getting those alignments done

preFIX – final teaser and release info

preFIX - gate and expander section with detailed sidechain fitering options

preFIX – getting those alignments done

getting those alignments done - finally is easy and fun

The upcoming preFIX audio plug-in was originally designed to meet the recording engineers needs and is all about audio alignment tasks: fix all that stuff that can’t be fixed outside the box (anymore) and do that fast and with highest quality right before the mixing starts itself.

preFIX is a pre-mixing and audio alignment tool which typically takes place upfront the mixing process. It provides a clever tool set to clean-up, fix and align audio tracks (typically taken from recordings) concerning overall frequency correction, phase alignment, spatial stereo field corrections and routing. It contains a complete gate/expander solution with a dedicated and comprehensive sidechain filtering path as well.

Though, preFIX is not only tailored to the recording engineers environment but delivers a truly great performance when shaping and lifting poor sample sources, sculpt electronic softsynth instruments or just by dialing in that super tight drum bus sensation as well.

those sexy curves again

proportional EQ curves

What constitutes those smooth sounding equalizers some are raving all about? In fact the answer is pretty much simple but maybe disenchanting to someone else: It’s in the equalizers transfer curve and (almost) nothing else. That equalizer transfer curve determines the actual frequency and phase response and generally speaking, in an analog filter model the frequency response implies the according phase response (and vice versa). In the digital domain this holds not true in general as shown by linear phase filter implementations. Additional effects like the actual transient response or additionally generated harmonics are then the icing on top (if desired) but may appear quite subtle or even negligible if we just look into rather transparent devices.

NastyDLA – final teaser and release info

NastyDLA – technical architecture

simplified technical architecture

Internally, NastyDLA consists of quite a bunch of DSP processing building blocks which as a whole are summing up to an authentic signal path simulation of it’s analog models. The blocks and the according signal flow are shown in the diagram above. Basic signal flow goes from left to right except the feedback path which goes in the opposite direction.

With NastyDLA, signal path coloration already starts in the input stage which provides a complete model of both, frequency and phase response as well as dynamic saturation. It’s located in the dry path but all nonlinear processing and coloring can be disabled on demand so it remains as a simple input volume control then. But while switched in, the input stage can greatly contribute on getting the processed signal to fit right into a mix.

quote of the day – phase shift

Quoted from the Manley Massive Passive EQ manual talking about “phase shift”:

“This is probably the most misunderstood term floating about in the mixing community. Lots of people blame or name phase shift for just about any audio problem that doesn’t sound like typical distortion. We ask that you try to approach this subject with an open mind and forget what you may have heard about  phase for now. This is not to be confused with “time alignment” as used in speakers, or the “phase” buttons on the console and multi-mic problems.”

I couldn’t agree more as already shown in the brief article on about audio signal coloration.

NastyVCS – released today

NastyVCS - Virtual Console Strip