R&D Stories: A DSP Audio Processor at the Heart

Have you ever ever had the chance to create one thing that’s really new? As a designer of a whole bunch of various merchandise over a few years, I can truthfully say not fairly often. Most of our merchandise are tweaks to current concepts which might be constructed on the data that we gained from our personal earlier designs and extra importantly, from others who maybe share our ardour.

That is the story of Danville Sign’s dspNexus DSP Audio Processor. Merely put, the dspNexus combines the standard position of a contemporary preamplifier (management heart) with a strong DSP crossover. As a lot as a lot of you might need to delve into the engineering particulars, this text will deal with the journey and the genesis of the dspNexus. I hope that a lot of you should have an opportunity to additional examine the dspNexus and draw your personal conclusions of whether or not we completed our targets.

 

The Journey
I don’t suppose I can inform the dspNexus story with out sharing somewhat of my private background and later the founding of Danville Sign.

In my youth within the mid-Nineteen Seventies, I joined a small workforce of gifted audio fans not so totally different than the viewers and contributors of audioXpress. I used to be a sophomore with {an electrical} engineering main. We began by modifying Dynaco preamplifiers and energy amplifiers, and we had some business success. By the tip of my junior yr, we began designing extra authentic circuits. Presently, I invented the cut up passive phono preamp, which was later patented. Modifying current circuits is like masking songs, creating new circuits is extra like writing your personal materials. Apart from studying a little bit of circuit idea, I feel the opposite ability I discovered from this collaboration was the power to hear critically, which is important for any good audio designer.

Within the early Nineteen Nineties, I designed noise discount merchandise utilizing Analog Units DSPs. I feel this was a reasonably pure transition for an analog engineer because the math is just not so totally different and the purposes usually overlapped. In 1998, I based Danville Sign Processing with the intent of constructing audio sign processing merchandise utilizing Analog Units DSPs. I designed my first SHARC-based DSP design in 2000 with a first-generation Analog Units’ floating level DSP. For my part, the SHARC is the gold normal of DSPs for audio processing.

After all, a village with one hut is just not a lot of a village, so now the story strikes to our workforce, since Danville Sign is now not a solo engineer and some subcontractors. Danville now has an engineering division so our merchandise evolve from a collective effort. We additionally manufacture all of our merchandise on our personal inside automated line in Cannon Falls, MN. This flexibility actually helps in the case of creating new merchandise.

Danville Sign’s buyer base has historically been aimed toward different producers, so that you will not be nicely acquainted with our merchandise. Since our clients are the model, we’re extra like “Intel inside.” However, we’ve possible infiltrated your audio world. Our DSP crossovers have been inside standard studio screens for greater than 10 years, which suggests a few of your music content material was mastered with our merchandise. We have now additionally supplied particular mastering electronics for vinyl urgent, DSP modules for beam forming in giant acoustic areas, DSP modules for a SOA CD participant, and DSP crossovers for high-performance client loudspeaker techniques.

 

DSP and the Digital Revolution
It must be clear to only about everybody that digital audio is the brand new regular. A lot of the content material that we routinely playback is both saved on an area music server or streamed from an Web supply. We’d additionally seize content material from a TV or telephone, which often is out there in a digital format. Because of this your playback system will want at the least one DAC.

Now I’ll make one other assertion: With the doable exception to value, there isn’t any benefit to a passive loudspeaker crossover. This has been recognized for a really very long time. I’ve a video on the Danville web site that discusses this challenge and you’ll find many different displays that current comparable arguments.

So when you settle for the earlier two assertions, I’ll declare {that a} good DSP-based energetic crossover is superior to an analog energetic crossover for the next causes:

• Content material might be already in digital format
• Filter complexity isn’t restricted given highly effective DSPs
• Non-compulsory FIR filtering
• Time alignment is straightforward and often fascinating
• Parameters are software program pushed and simply adjustable
• Stability of efficiency
• Look forward limiters are doable
• Danville Sign and the large-space skilled acoustics market has embraced this concept for fairly a while. From their perspective, the power to steer arrays, align techniques in time, and so forth are compelling arguments for DSP.

The small-space skilled market (recording studio screens) has now additionally embraced DSP crossovers as a fascinating function in most high-quality studio screens. On this market, most audio system are already powered, so including a DSP internally doesn’t change the shape issue.

The high-end client market has been the slowest to undertake, however that is altering. I bear in mind inadvertently assembly a reviewer from Stereophile in an elevator at CES round 2014 or 2015. He requested me what we did and I mentioned: “DSP Audio.” His response was, “You should be very busy.” This was clearly a change from early years the place DSP was extra suspect. I feel the tipping level began round 2016 when shoppers began asking speaker producers if their merchandise use DSP crossovers.

 

The dspNexus Thought Takes Type
Danville had been manufacturing a primary DSP field for a number of years known as the dspMusik 2/8. It began out as quite simple field that had selectable stereo inputs: balanced analog, USB Audio Class 2, and S/PDIF. It had eight balanced audio outputs, making it nicely appropriate for DSP crossover purposes.

audioXpress highlighted it in a difficulty a yr in the past. Internally, it had a SHARC DSP that was working DSP Ideas’ Audio Weaver, a strong GUI-based design device that permits you to drag and drop optimized DSP modules to create the sign processing wanted for the DSP crossover and different sign processing features. The power of the dspMusik was that it was most likely probably the most highly effective and finest sounding DSP crossover out there on the time. It used prime performing AKM ADC and DACs.

Sooner or later I used to be visiting Wealthy Hollis of Hollis Audio Labs (HAL). Wealthy makes some excellent planar magnetic line arrays that used a dspMusik because the crossover. We had been invited to a demo at considered one of Wealthy’s native clients. This technique sounded nice! Not surprisingly, it had a stack of fantastic energy amplifiers, fats costly cables, and a music server all residing in a really good room. In the midst of every little thing was this humble dspMusik 2/8, working the entire system. It was clearly time to rethink the dspMusik with a brisker strategy.

Wealthy and I began defining what would in the end grow to be the dspNexus platform. The dspNexus goal market is primarily speaker producers and severe loudspeaker DIYers who need to create the best performing loudspeaker techniques. You actually can’t do that with no fashionable energetic DSP crossover. Because of this a loudspeaker producer utilizing this strategy wants an answer that’s simply tailor-made for the particular necessities of the goal loudspeaker. Most dspNexus techniques offered to finish customers can be preconfigured for a particular model and mannequin. We might provide DSP Ideas’ Audio Weaver.

We envisioned a product that may by no means apologize for its audio efficiency. This instructed that almost all key elements could be constructed as replaceable modules. In the present day’s finest DSPs, ADCs, and DACs are tomorrow’s second finest. To this finish, it additionally meant that every module would have read-back functionality in order that as new modules are created, we might routinely decide what was plugged into the motherboard and adapt accordingly. This additionally required the product to be software program upgradeable with out particular programming instruments.

It was clear that we would have liked to improve the enclosure to be a lot bigger and extra engaging. Within the high-end audio market, there was a little bit of an arms race to make enclosures with extremely thick entrance panels and glossy mirrored surfaces. This vastly will increase manufacturing value, with none profit to efficiency. We thought the dspNexus wanted to look good {and professional}, however we weren’t aiming for bling.

In some ways, this a part of the conceptualization course of and later the precise implementation was the simple half. We already knew easy methods to make the DSPs, ADCs, DACs, and supporting circuits work nicely. This space is our firm’s core competency in any case. If this was our complete aim, we might have simply repackaged a dspMusik, however we actually needed to rethink easy methods to make a preamplifier/management heart that may be related to fashionable stereo techniques.

In at the moment’s world, audio sources come from many locations. We settled on the next enter sources as an inexpensive set to accommodate most wants:

• Balanced Audio Inputs
• USB Audio Class 2
• S/PDIF
• Bluetooth with aptX HD help
• Wi-Fi
• Ethernet

We determined so as to add a headphone amplifier as a result of it was clear that typically individuals need to hearken to music when others might not need to share their expertise (maybe they’re sleeping?). The headphone amplifier wanted to match nicely with different high-quality headphone DACs. Since many of the supporting circuits would exist already within the dspNexus, this was actually only a matter of making a small energy amplifier with applicable sign routing.

Maybe the largest departure from a standard preamplifier is that we determined to combine a Raspberry Pi 4 (RPi4) small board pc (SBC). The RPi4 has very broad help and is more likely to be out there for a few years. This made it the SBC of selection over comparable gadgets.

By including the RPi4, we opened the door to working purposes within the dspNexus. This might be for speaker measurement packages, music server, or room correction/bass administration. It additionally might operate as a bridge for exterior Wi-Fi or Ethernet sources. Within the dspNexus, an area SHARC DSP does the principle sign processing, so the RPi4 is simply one other peripheral.

 

Many purchasers are going to make speaker measurements, so we added a phantom-powered microphone enter. It’s also doable to measure delay from every DAC to the microphone. This enables relative time delay to be measured in a buyer atmosphere for aligning subwoofers, because the placement of a subwoofer could be unknown till set up.

Frankly, the one function we added that I feel may be heresy for some customers, is that the ADC module will be configured as a phono preamplifier entrance finish. The differential enter impedance is 47kΩ. It additionally has load capacitors that may be switched for cartridge loading. This units the stage for a DSP phono preamplifier for transferring magnet cartridges or transferring coil cartridges with an exterior transformer or pre-preamplifier. In precept, this opens the door to pop elimination since we will have a look at the output of the phono cartridge earlier than equalization and delay it a small quantity. This may enable the pop to be eliminated earlier than it was too late to snip out. Regardless, it is going to be enjoyable to play with a DSP phono preamplifier implementation.

The primary dspNexus items are transport to earlier adopters. We’re excited concerning the dspNexus and its distinctive set of capabilities. Because it makes use of modular building and is software program upgradeable, the dspNexus will proceed to enhance as we transfer ahead. Get your fingers on one and tell us what you suppose in addition to what you’d wish to see in future upgrades. 

This text was initially revealed in audioXpress, November 2021.

Concerning the Writer

Al Clark is the co-founder and CEO of Danville Sign Processing. As one of many 4 founders of Van Alstine Audio Techniques, Al launched his profession 45 years in the past as an analog engineer. This firm made high-end preamplifiers and energy amplifiers within the mid-Nineteen Seventies. He began designing DSP-based merchandise with first-generation DSPs within the late Nineteen Eighties and has since created extra Analog Units’ SHARC-based DSP boards than anybody else on this planet. He has a Bachelor of Electrical Engineering diploma from the College of Minnesota and is a life member of the Audio Engineering Society.