With the HEDD Lineariser® plugin, we have created a unique solution for one of the most challenging problems in the history of loudspeaker designing: Linear Phase Response. What does it mean and why will your HEDD studio monitors sound better than ever?

Well, all loudspeakers regardless of size or construction cause phase errors. This means that not all frequencies leave the speaker at the exact same point in time. This has to do with physics: The fundamental relation between time and frequency is expressed by the so-called Fourier Transform, which explains that corrections in the frequency domain will inevitably alter the phase response – and vice versa. You can’t have both, linear frequency and phase response at the same time, at least not in an analog loudspeaker design.

The above said is true for complete speakers as well as for some of its ingredients. Think of a monitor as a complex network of different filters. The voice coils for an example are low pass filters in itself, and so is the volume of a cabinet. A tweeter sends out high frequency material significantly earlier than midrange and low frequency drivers – another source for phase problems. All these timely aberrations vary with frequency and together they build the phase response of the complete loudspeaker. Phase problems can make a speaker’s stereo image sound somewhat mushy and undefined.

 

Ideally the phase response should be displayed as a straight line, indicating a perfect timely relation between the different sound layers emanating from the speaker.

When DSPs arrived at the end of the 1970’s, many traditional problems of loudspeaker designing could be reappraised. Because in the digital domain, DSPs can collect the incoming data stream, divide it into blocks and store it for a moment. It is precisely this moment where the limitation of Fourier transform is overcome and real progress starts. Today’s computers allow to store an arriving signal long enough to wait for the slower low frequencies to arrive. If the computer has exact measurements from a specific speaker it can anticipate the upcoming delays and apply advanced FIR (Finite Impulse Response) filtering to create linear phase response. In fact, FIR filtering makes it possible to deliver the desired linearity both in the time and the frequency domain.

While 99% of current DSP-based speakers offer only basic IIR filtering, HEDD applies the latest FIR technology to perfect the speakers in their timely behavior. Nothing less.

A plugin to perfect your HEDD monitors in the time domain

 

The HEDD Lineariser® plugin makes FIR technology viable for HEDD’s present and future monitors, without forcing the loudspeaker into an additional AD/DA conversion (your signal will not be degraded).  What is more, the HEDD Lineariser® is run by CPU power which nowadays exceeds any DSP when it comes to precisely calculating the audio signal during processing. During mixdown, recording, mastering or simply playback, the HEDD Lineariser® gives you the following choices:

HEDD-Lineariser

Bypass for rendering

A reproduction with linear phase occasionally can show higher peaks than the original waveform. To avoid overloads during filtering the gain is reduced by 9 dB. To allow 1:1 rendering, a hard bypass (called Bypass to render) is possible (in addition to the In / Out  option), it allows rendering the original file without changes of any kind.

MODEL

Each HEDD monitor is carefully measured in the large anechoic chamber of the Technical University in Berlin. The individual impulse response serves to linearise the respective model both in time and frequency.

HEDD alignment curve
This setting represents what we consider to be the ideal sound for normal listening rooms. It exhibits a bass response identical to the analog HEDD design.

Anechoic flat curve
Based on 1m measurements in an anechoic room, this setting leads to a different bass response.

PHASE

Linear full range  – Latency < 100 ms
Phase response is linearised from 30 Hz – 40 kHz with deviations < ±1°. Recommended for mixing, post-production, and normal playback.

Linear above 500 Hz – Latency < 5 ms
Phase linearisation starts above 500 Hz only. This setting better suits recording situations.

Minimum Phase – Latency < 2 ms
No phase linearisation is applied, however frequency response – like in all other cases – becomes flat to ± 0,5 dB. There is practical no latency in the signal path.

When activating the HEDD Lineariser® in your DAW or as a standalone application, transients are reproduced in perfect accuracy and the spatial qualities are being increased. Acoustic recordings will impress with their natural and intriguing character.

Before and after the Lineariser®: Measurements

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Type_30_Impulse_Response_HA
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HEDD Type 30: Frequency and phase response (grey: without, blue: with Lineariser® engaged)

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System Requirements: Windows (7, 8, 8.1, 10, x86, x64) – Mac OSX 10.8 or newer. The Lineariser® is available in VST, AU, and AAX format.