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miniDSP 2x4

Frankly, I'm not really interested in rabbit trails about DCX2496 at the moment, despite having one. Sorta been there, done that over the years.

The miniDSP, topic of his tread and something else I personally own and use, is being harshly critiqued so I think that should remain 100% of the focus.
 
robgmn said:
A hard and fast conclusion with minimal study.

I have no dog in the race (I enjoy learning through discussion as opposed to just reading), but have you tested multiple units?
Have you tested with sine wave versus square wave (my knowledge of the science is minimal, but I thought music would be a sine wave)?
Is it possible that no one (not even the mfgr.) has ever done a scientific test on a MiniDSP, and you have revealed the Emperor's new clothes (wouldn't be the first time something like that happened)?
Will you be sharing the pictures of your test results?
Are you going to reveal the info on the other equipment used (speaker mfgr/model, preamp model, music source, equipment connection layout, etc.)?

Inquiring minds (well, mine anyway) want to know!
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I only tested this unit. But the other 2 units (not lab tested) sounded the same.

Music can be like sine waves. But also can be jagged like a square wave. A single instrument is more like sine wave. A large group of instruments playing together can sum up to a waveform that for some instants can be like a square wave or worst.

A square wave represents the most difficult waveform to reproduce and my choice as test signal.

The equipment used was an HP209A and GW Instek GDS1054B. For listening, two HP467A with custom made 2 way nearfield monitors.

Fixed the image permissions.
 
I can say with certainty it isn't an anomaly, new or otherwise, that the output signal level can be approximately 1/2 of the input level.

For some time now the miniDSP unbalanced has the option of 0.9V or 2.0V input sensitivity, while the output is always max of 0.9V. So, if the input sensitivity of the one being tested is set to 2.0V that is the explanation of why the output measures about 1/2 of the input (45%, technically, I suppose, considering 0.9 / 2.0).

This is done for compatibility with front end gear of various gains and is well-documented on the miniDSP website and instructions.
 
whoaru99 said:
I can say with certainty it isn't an anomaly, new or otherwise, that the output signal level can be approximately 1/2 of the input level.

For some time now the miniDSP unbalanced has the option of 0.9V or 2.0V input sensitivity, while the output is always max of 0.9V. So, if the input sensitivity of the one being tested is set to 2.0V that is the explanation of why the output measures about 1/2 of the input (45%, technically, I suppose, considering 0.9 / 2.0).

This is done for compatibility with front end gear of various gains and is well-documented on the miniDSP website and instructions.
Click to expand...

Just re-tested the miniDSP and found out that there is not a compression problem. The compression I saw was caused by the attenuator I used to reduce the signal from the oscillator.
 
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Tested the Behringer Ultra Curve Pro.
Compared to the miniDSP the Behringer is quieter, can handle very large signals before clipping, and the delay is longer. I did not took any images.

FYI: I made edits to several of my posts in this thread because I made a mistake when observed compression which was caused by an attenuator before the device under test.

My conclusion has shifted: The miniDSP 2x4 (not HD) will add distortion and noise to the signal, a bit more than a competing model from behringer. So, for what it is, I guess is as expected.
 
Retested the miniDSP 2x4 and the Behringer Ultra Curve Pro. Also tested an old Samsom 31 band EQ.
All EQs were set flat. No bypass, all EQs were engaged.
All did better than my miniDSP
The Behringer, produced similar digital artifacts but maxed out at about 12 Vpp.
The old analog Samsom passed a near perfect square wave at 1Khz without any noticeable noise, and its output never clipped up to my source max of 20 Vpp.
 
AngelRa said:
A square wave represents the most difficult waveform to reproduce and my choice as test signal.
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It is also the test signal used by many in the audio press to test equipment. It reveals a lot about the system. There are many ways to read square waves beyond what we interpret by simply looking at them.
 
AngelRa said:
I used my B&K 3384 reference mic, an UMC 202 24/192 audio interface. Proceeded to create correction curves and sent them to the miniDSP. There was not much to fix so the curves were mild, almost flat.
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I'm curious...I've never heard of that B&K capsule model (usually they are 4XXX models) are you talking about one of their SPL meters with an attached pre-amp + capsule or maybe a Pulse front-end system? What's the frequency response?

Great analysis. Love that you're using a wideband HP amplifier for audio reference haha. Good stuff! I'm guessing you work as test engineer of some kind?
 
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AngelRa said:
My conclusion:

The miniDSP 2x4 distorts and create sound artifacts.
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I interpret your results rather differently.

What you've described as a "3khz square wave" is what I would describe as a 3khz pulse rate. It actually represents a much higher frequency than 3khz, because bandwidth is defined by the slope of waveform, not the pulse rate. An ideal square wave has a perfectly vertical slope on the sides, which represents an infinitely high bandwidth; the result of summing an infinite series of odd-harmonic sine waves of diminishing amplitude up to infinite frequency.

Obviously, an ideal square wave is not achievable in practice, but depending on what you used to generate the square wave, you may actually be feeding the miniDSP a signal that represents bandwidth into the hundreds of kilohertz, megahertz, or even gigahertz. The miniDSP is an audio digital device and not designed to handle such radio frequency sampling, and is therefore likely bandwidth-limited to a bit above 20khz, which is almost certainly a far lower frequency than what is represented by your square-wave input.

That's why the output of the miniDSP shows what you've described as oscillation. It's not oscillation. It's actually the miniDSP's attempt to model an input frequency far beyond its bandwidth limits. It looks almost exactly like Figure 2.39 from http://digitalsoundandmusic.com/2-3-3-modeling-sound-in-matlab/ -- which shows a square wave modelled from the sum of eight sine waves -- because you've effectively forced the miniDSP to model a square wave from a finite set of sine waves with frequencies up to its bandwidth limit.

Therefore, a better test would be to bandwidth limit your square wave to 20khz with a low-pass filter, and use the output of the low-pass filter as the input to the miniDSP. That would provide a far more accurate test of the miniDSP's ability to represent real audio input.
 
Gibbs Phenomenon.

SquareWave.gif


And, with the standard miniDSP sampling frequency of 48kHz, the noted performance is not unexpected with square waves as Dave mentions.

The HD versions sample 96kHz so would do better but still exhibit the phenemona on non-bandwidth limited square wave.
 
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rifftrax said:
I'm curious...I've never heard of that B&K capsule model (usually they are 4XXX models) are you talking about one of their SPL meters with an attached pre-amp + capsule or maybe a Pulse front-end system? What's the frequency response?

Great analysis. Love that you're using a wideband HP amplifier for audio reference haha. Good stuff! I'm guessing you work as test engineer of some kind?
Click to expand...
the mic is a 3384, it is very small, all stainless body.
 
AngelRa said:
Thanks for the info. Yes I refer to the Gibbs which appear larger in amplitude than in other devices.
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That only means the bandwidth limit is different from other devices. Without identifying, measuring, and/or allowing for that limit, noting that it varies from device to device doesn't tell us anything.
 
DaveVoorhis said:
That only means the bandwidth limit is different from other devices. Without identifying, measuring, and/or allowing for that limit, noting that it varies from device to device doesn't tell us anything.
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Still, I can hear a clear degradation.
The jumpers in the unit are set for 0.9 volts, the output is about half of the input. Is that normal? I am starting to guess the problem lies in over driving the unit.
 
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