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#395150 - 07/15/13 02:55 PM Broadband DSP Correction
Ian Offline
President
aficionado

Registered: 03/13/01
Posts: 774
The introduction of the LFR1100 brought about a lot of questions about using a Broadband Digital Signal Processor (DSP) between your pre-amp and your main amp in other speaker models for the purpose of smoothing out small anomalies in the amplitude response. These are referred to as ‘High Q’ corrections to the response curves.

In many ways a speaker’s amplitude response curve could be divided into two Q groups:
• The Low Q, which deals with amplitude differences over a wide frequency band
• And the High Q, which deals with amplitude differences within a narrow frequency band.


Audibility of small differences in amplitude over a wide frequency band (Low Q) is very noticeable and needs to be carefully addressed in the design on the speaker. On the other hand, audibility of small differences in amplitude over a narrow frequency band (High Q) is not very audible. The DSP in the LFR1100 already incorporates this High Q correction across the frequency band. Low Q correction is done in using the passive crossover network located inside the cabinet.

In response to all these inquiries we have created a DSP component that is able to do this High Q correction to the M80v3, VP180v3, VP160v3, and recently announced M100. The graphs below show the difference in the Listening Window response to an M80v3. Since the correction applied from the DSP is concentrated completely in the High Q group we would recommend this product for the discerning audiophile only as the audibility of this correction will be quite subtle.

The other feature on the DSP for the LFR1100 is the Boundary Switch, which is used to compensate for having your speakers very close to walls or large cabinets. Even though the M80s and M100s are not omnidirectional the proximity to boundaries still does have an effect in the lower frequencies. For that reason we have included a Boundary Switch on the DSP for these models also which should be experimented with in your room as the effect of the rear wall proximity will vary from room to room.

We will have these DSP Correction boxes available at the end of August. For anyone purchasing one of these to be used with their current M80v3 and VP180v3 we will need you to provide us with the serial numbers as there have been modifications to them along the way. We have created a spot to do this during the order process. The cost of the DSP box will be $950 for your two main speakers and $1,260 if you wish to add another DSP in the box for your VP180 or VP160. We will be doing a pre-release promotional price of $690 and $890 respectively from now until the end of July.

Broadband Digital Signal Processor

Uncorrected M80


Corrected M80

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#395163 - 07/16/13 02:14 AM Re: Broadband DSP Correction [Re: Ian]
brwsaw Offline
aficionado

Registered: 10/12/12
Posts: 858
Would the difference be more pronounced on lower quality recordings, radio broadcasts etc?

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#395164 - 07/16/13 04:30 AM Re: Broadband DSP Correction [Re: brwsaw]
Ian Offline
President
aficionado

Registered: 03/13/01
Posts: 774
The difference should remain the same no matter the type of recording you are playing.
_________________________
Ian Colquhoun
President & Chief Engineer

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#395168 - 07/16/13 09:42 AM Re: Broadband DSP Correction [Re: Ian]
ClubNeon Offline
connoisseur

Registered: 02/06/09
Posts: 3447
Loc: Western Maryland, USA
I guess this is as good a thread as any to ask about a particular technical detail of the DSP box.

At what sampling rate does it operate internally? And how does it deal with any input signal that is at or above it's Nyquist limit?

I'm perfectly OK with a sampling rate in the 40 kHz range. Though, unless there's a steep decimation filter before the ADC, any Blu-rays foolishly encoded at 96 or 192 kHz may cause audible aliasing artifacts when resampled at that lower rate.
_________________________
Pioneer VSX-1018AH-K, PDP-5020FD, DV-79AVi
Axiom M22s, VP150, QS8s
Sony PS3, surround backs
-Chris

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#395170 - 07/16/13 10:27 AM Re: Broadband DSP Correction [Re: ClubNeon]
Andrew Offline
Axiom Engineer
veteran

Registered: 12/18/01
Posts: 164
Originally Posted By: ClubNeon
I guess this is as good a thread as any to ask about a particular technical detail of the DSP box.

At what sampling rate does it operate internally? And how does it deal with any input signal that is at or above it's Nyquist limit?

I'm perfectly OK with a sampling rate in the 40 kHz range. Though, unless there's a steep decimation filter before the ADC, any Blu-rays foolishly encoded at 96 or 192 kHz may cause audible aliasing artifacts when resampled at that lower rate.


Hi ClubNeon,

As you are likely aware, there are three main components to the processing chain inside the DSP box: ADCs, DSP core, and DACs. Both the ADCs and DACs are Sigma-Delta, 24-bit, and operating at a 96kHz sampling rate. Inside the DSP core itself most of the processing instructions are double precision, 56-bit (28-bit × 28-bit multiplier with 56-bit accumulator). The DSP core is capable of performing 50 MIPS and we are utilizing a fraction of the available headroom. There is an active anti-aliasing filter at the input to the ADCs.

I hope that answers your questions!

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#395172 - 07/16/13 11:31 AM Re: Broadband DSP Correction [Re: Ian]
ClubNeon Offline
connoisseur

Registered: 02/06/09
Posts: 3447
Loc: Western Maryland, USA
Not only did that answer my question, it's the answer I wanted to hear. laugh
_________________________
Pioneer VSX-1018AH-K, PDP-5020FD, DV-79AVi
Axiom M22s, VP150, QS8s
Sony PS3, surround backs
-Chris

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#395177 - 07/16/13 01:14 PM Re: Broadband DSP Correction [Re: Ian]
tomtuttle Offline
axiomite

Registered: 06/20/03
Posts: 8142
Loc: Tacoma
If Chris is happy, then I'm happy.

Geeks.
_________________________
bibere usque ad hilaritatem

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#395396 - 07/22/13 04:42 PM Re: Broadband DSP Correction [Re: Andrew]
Charles65 Offline
frequent flier

Registered: 07/22/13
Posts: 14
So what this DSP box is doing is to convert the analog signal in digital (with the ADC chip), process it, and reconvert to analog (with the DAC chip) and give the corrected signal back to the amp?

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#395397 - 07/22/13 04:51 PM Re: Broadband DSP Correction [Re: Charles65]
Charles65 Offline
frequent flier

Registered: 07/22/13
Posts: 14
P.S. So will it have a direct digital entry or only an analog entry? Would be nice to see the back of the box on this page: http://www.axiomaudio.com/broadband-digital-signal-processor#

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#395427 - 07/23/13 01:07 AM Re: Broadband DSP Correction [Re: Ian]
cohesion Offline
veteran

Registered: 03/27/12
Posts: 159
Loc: Maple, Ontario, Canada
The one for my LFRs only has analogue (though both RCA and XLR). I can't see how this would change in the new version. In fact the specs only mention the RCA and XLR inputs.

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