Is Good DAC Still Necessary With DSP Sound Processor?

[badman]

A voice of sanity. I involuntarily laugh or facepalm, depending on my mood, whenever someone tries to improve on the theoretical work of Harry Nyquist. Those who consider themselves Golden Ears get pretty defensive when faced with engineering facts. At that point what follows reminds me of fairy tales.

As for digital volume controls in DACs throwing signal away, the one I use will if I attenuate more than, I think it is, 55dBs. Who turns down their system 55dBs?

Reviving a Zombie Thread since this is some of the most lucid thinking I've seen on the subjects. Great stuff guys.

I am reintegrating some DSP, specifically a DBX Venu360, into my rig. The above conversation has been en-pointe for the most part, but I want to address this above 55dB issue-

I regularly turn down my system 55dB or more, and have spent a lot of time with attenuation in various forms trying to maintain resolution and low noise. I've made transformer volume controls of multiple types, as well as buffers, traditional preamps and resistive attenuators. For the DSP, my input levels will be exceedingly low if I don't work around that issue. The problem is that high efficiency speakers, coupled with powerful and sensitive home amplifiers (without any input trimmers) will operate in home spaces at very low output relative to their maximum. I have some 200-500 "real" watts per driver available and most of my drivers are generally 97dB or more, in a modest space. I prefer the sound of big efficient systems (as we tend to around here), but it means that typical gain structures are way too much.

The solution is well known to many in the pro/venue space, where it's generally a mixer or the like feeding the DSP. Input trimmers on amplifier inputs allow you to structure your gain differently, so that you can avoid pushing against either the noise/resolution floor or potential clipping. The former is usually able to be fixed easily by adjusting the trimpots on amplifiers downward and the mixer master volume upward, leading to a higher voltage throughput on the DSP, and better noise and quantization performance. If you're clipping the mixer to get that voltage, you done gone too far, and you need to back off the mixer volume and up the trims on the amps.

So for me, I've spent the last day deciding around some of what I'll do to correct the issue- I've been waffling between two options:

1. Simple DIY resistor networks, either as part of cables, or wired on the input XLRs of the amps
2. Having someone else do it for me- https://naiant.com/custom_audio_repr...nline-devices/, either as an adaptor attenuator or built into some cable.

There are cheap XLR attenuators on market but they do not seem to be of sufficient quality for my taste, with many designed around 600 ohm operation (too low) or not properly balanced (an L-pad on just one leg of a balanced connection will lower the volume of a differential input, but isn't ideal). Naiant doesn't seem to suffer from any of those issues, and the adjustable units are very, very cool.

One can also change the gain structure as another way to get down that path, but the point is, where your gain takes place in a system with ADC is very important, and 55dB isn't an unheard of level of attenuation.

[David Ketley]

Reviving a Zombie Thread since this is some of the most lucid thinking I've seen on the subjects. Great stuff guys.

I am reintegrating some DSP, specifically a DBX Venu360, into my rig. The above conversation has been en-pointe for the most part, but I want to address this above 55dB issue-

I regularly turn down my system 55dB or more, and have spent a lot of time with attenuation in various forms trying to maintain resolution and low noise. I've made transformer volume controls of multiple types, as well as buffers, traditional preamps and resistive attenuators. For the DSP, my input levels will be exceedingly low if I don't work around that issue. The problem is that high efficiency speakers, coupled with powerful and sensitive home amplifiers (without any input trimmers) will operate in home spaces at very low output relative to their maximum. I have some 200-500 "real" watts per driver available and most of my drivers are generally 97dB or more, in a modest space. I prefer the sound of big efficient systems (as we tend to around here), but it means that typical gain structures are way too much.

The solution is well known to many in the pro/venue space, where it's generally a mixer or the like feeding the DSP. Input trimmers on amplifier inputs allow you to structure your gain differently, so that you can avoid pushing against either the noise/resolution floor or potential clipping. The former is usually able to be fixed easily by adjusting the trimpots on amplifiers downward and the mixer master volume upward, leading to a higher voltage throughput on the DSP, and better noise and quantization performance. If you're clipping the mixer to get that voltage, you done gone too far, and you need to back off the mixer volume and up the trims on the amps.

So for me, I've spent the last day deciding around some of what I'll do to correct the issue- I've been waffling between two options:

1. Simple DIY resistor networks, either as part of cables, or wired on the input XLRs of the amps
2. Having someone else do it for me- https://naiant.com/custom_audio_repr...nline-devices/, either as an adaptor attenuator or built into some cable.

There are cheap XLR attenuators on market but they do not seem to be of sufficient quality for my taste, with many designed around 600 ohm operation (too low) or not properly balanced (an L-pad on just one leg of a balanced connection will lower the volume of a differential input, but isn't ideal). Naiant doesn't seem to suffer from any of those issues, and the adjustable units are very, very cool.

One can also change the gain structure as another way to get down that path, but the point is, where your gain takes place in a system with ADC is very important, and 55dB isn't an unheard of level of attenuation.

I now use a lightspeed attenuator as my main control and noticed an immediate increase in bass control, I guess a better impedance match. Now I am going to contradict myself, my Lampizator DAC went faulty so in desperation I hooked the system up direct to the computer and am amazed at the sound its producing. It is a high end Laptop but its not supposed to sound that good!!!!!! Another problem one of the amplifiers also decided it had enough and started smoking. Again in desperation to have something to listen to I connected my old Denon RCD M37DAB driving the compression drivers. Another revelation, I had never heard such clarity from the top end. My old Yamaha M60 amp is going up for sale but as its switchable Class A its going to be difficult to replace maybe try a Chinese offering?

[badman]

I now use a lightspeed attenuator as my main control and noticed an immediate increase in bass control, I guess a better impedance match. Now I am going to contradict myself, my Lampizator DAC went faulty so in desperation I hooked the system up direct to the computer and am amazed at the sound its producing. It is a high end Laptop but its not supposed to sound that good!!!!!! Another problem one of the amplifiers also decided it had enough and started smoking. Again in desperation to have something to listen to I connected my old Denon RCD M37DAB driving the compression drivers. Another revelation, I had never heard such clarity from the top end. My old Yamaha M60 amp is going up for sale but as its switchable Class A its going to be difficult to replace maybe try a Chinese offering?

You may be doing that very human thing of "new"="improved". It's very common in this hobby to hear a change as an improvement by default, which is part of why people seem to always upgrade over and over and over, even though at each point they tell themselves "I'm done, this is amazing".

Regarding amp, I don't know your budget, but I am a serious advocate of hypex NCore amplification. Nord Acoustics is an excellent and fairly priced source for pre-built, in any configuration you can imagine. It's not cheap stuff but it's world class amplification.

[sebackman]

Hi,

Not knowing how your signal chain looks like it is in general a bad idea to introduce "resistors" in the signal chain unless the source is very low impedance and the "reciver" is high impedance. If the source is "pro" ie <600ohms output it is usually fine within limits. I concur with previous posts that you should keep the level into the DSP (if analogue) as high as possible to maintain decent S/N and that may post a problem later in the chain if there are no input trimmers as stated.

Is this 2-channel or multi, active or passive speakers? Are you running balanced cabling?

There are several attenuator alternatives in the "pro" market, both passive and active.

I'm on a fully digital chain with separate multi Burr&Brown VCA's after the DAC's but the newer BSS units do provide a good attenuator function that can be controlled from any iPhone or iPad. They use 41 bit internally which provides for retained resolution even when reducing volume in the digital domain. Most other DSP's does not. In fact, many of them are direct poor in volume control as they do it in or before the DAC chip (usually 16 or 24 bit) and not in the DSP chip (often up to 41 bits FP). Some use analogue VCA on the output which is muck better if correct implemented. Or just a pot for gain control. BSS solved this by implementing attenuation as a DSP function and it is just a nice feature that you can control it via (AA) via an app (iPhone/iPad) or indeed even by a single analogue hard wired pot attached to the rear of the BSS.

Even if that is not what you want to hear I would sell the DBX and get a BSS BLU160 (or BLU100-103 which is fixed IO), feed it digitally via an digital input card or use the BSS BLU-USB which is a very good asynchronous sound card with USB in and digital BSS BLU-LINK out (I have both). The beauty with BLU-Link is that the BSS sound card will use the BSS BLU-XXX DSP clock via BLU-LINK and as it is asynchronous the potential limitation from the computer OS i limited. This would give you up to 256 channels out @48kHz. I would then use the BSS digital volume control controlled via iPhone or iPad and feed analogue signal to your power amps.

There is currently no other simple solution to a fully digital DSP/active crossover chain with working volume control in the market today, at reasonable price. There may be separate DAC's in the market with good volume controls implemented (digital or analogue) but the problem will be to calibrate levels and to control all of them at the same time if more than 2 channels. I've seen some attempts but not really any successful solutions.

The balanced Burr&Brown VCA's (2 x 8 channels) I'm using cost an arm and half a leg at the time and was introduced before I went with BSS. Today I would use the BSS volume control to control volume to my 8+8+2 power amps (3-way active 5.2). That is also what JBL is using in the Mark Levinson M2 package (the JBL DSP SDSC's is a re-badged BSS)

Kind regards
//Rob

[Ian Mackenzie]

Hi Rob,

Are those and BSS BLU160’s (or BLU100-103) the ones that make so much fan noise they become an annoying?

I recall this discussed in a thread sometime back.

[sebackman]

Hi Ian,

Sure is. However you can mount silent Noctua fans or a slow 120mm fan and be done. Even in a quiet living room.

Some use them without cover and the fans disconnected. Seems to work fine.

Alternatively use a BLU50 without any fan and add BLU BOB’s BLU BIB’s to get desired number of output and input channels. No fans at all.

Kind regards
//Rob

[Ian Mackenzie]

There must be an easier way surely.