Monthly Archives: October 2017

Public Schools and Groceries

As a society we’ve chosen not to let poor people starve. Anyone who cannot afford to feed himself is provided food by the government, funded by taxpayers. But to do this, we don’t have the government running farms and grocery stores. Instead, the government gives people money or food stamps to buy food at the same places everyone else does.

This makes sense because the market economy organizes farms, transportation, and distribution of food far better than government ever could. Indeed, this system works so well, it makes food so abundant and inexpensive that obesity is far more common than malnutrition!

So when our society decides every kid should get a decent education even if his family can’t afford it, why do people assume this means the government has to create and operate schools? Why don’t we let the market economy organize education and give poor people money or vouchers to attend the same schools everyone else does?

Everything I’ve read about economics and education suggests this would work much better. We’d have higher quality education, with greater variety of methods better tailored to the individual needs of students and families, more accountable to families, delivered at a lower price.

Consider the incredible variety at your local grocery store. Not only is food abundant and inexpensive all year-round, coordinated with farmers who grow it world-wide in a complex, efficient distribution network. Yet it also meets the unique needs of small minorities: foods for diabetics, vegans, kosher or halal, etc. In contrast, the 20th century has demonstrated that when governments attempt to operate or micromanage the farming and distribution of food it leads to mass starvation.

It is only fair to assume people on all sides of the debate have good intentions. Just because someone questions public schools, doesn’t mean he is against education, or thinks education should favor the wealthy. Au contraire! The current system of public schools all too often condemns poor people to terrible schools because they live in low-income areas, while wealthy people have better public schools and also the option to send their kids to private schools that only they can afford. These problems result from our government operating schools. That’s unnecessary and counterproductive. Letting the market organize independently operated schools and giving poor people money or vouchers to attend the school of their choice would improve schools and make them available to ALL kids and families.

JDS Element vs Meier Corda Jazz

This is a detailed comparison of the Corda Jazz with the JDS Element. I own one of each and listen to them almost every day, along with an Oppo HA-1. I’ve reviewed each of them separately.

TL;DR Summary: If all you need is a pure analog headphone amp, get the Corda Jazz. It has all the clean neutrality of the JDS Element, but richer, sweeter, more refined. If you want the flexibility of having a DAC and analog RCA inputs and outputs too (even if you won’t always use them), get the JDS Element.

Similarities

Cost: Both cost the same (about $350).

Provenance: Both are built by very small independent companies. Both are designed and built with a no-bullshit engineering philosophy.

Sound Quality: Both have excellent sound quality both subjective and measured that could be considered “reference” from an objective perspective, meaning it’s hard to differentiate them from each other, or from top end reference gear in a properly done level matched DBT. Of course, that doesn’t mean they sound the same (they don’t). In my opinion, they’re in the same league as the best gear I’ve heard costing a lot more, and their relatively low price is the only reason they might not be considered “audiophile” in some circles.

Gain: Both have adjustable gain separate from the volume knob–a switch for high vs. low gain. This enables them to drive anything from efficient IEMs that only need millivolts and milliwatts, to big power hungry planar magnetics.

Power: Both have > 1 watt max continuous power output, enough to drive almost any headphone on the planet, except for electrostats which need a dedicated voltage step-up transformer.

Reliability: I’ve used both near daily for more than a year with no problems.

I believe any pragmatic audiophile (myself included) would be delighted with either one, so long as he valued sound quality and neutrality over fancy knobs, glowing displays and the exclusivity of limited production boutique equipment. Actually, each of these does provide some of the latter exclusivity despite their low price, being less common than mass-produced gear from major manufacturers. When people see one on your desk they ask, “What the heck is that?”

Differences

DAC: Advantage: JDS Element
The Element has a DAC; the Jazz doesn’t. The Element’s DAC is clean, but USB-only and does not run in async; it relies on the source (your computer) to clock the data. JDS claims async mode doesn’t provide any audible benefit, and their measurements support that claim (though that doesn’t necessarily make it true). I do note, when using theĀ  Element, occasional “tics” or brief drop-outs that are not in the source material and occur seemingly randomly. This is consistent with the notion that the clocks (computer source vs. Element DAC) are slightly different and it occasionally re-syncs. This may happen less frequently or never on other computers.

Flexibility: Advantage: JDS Element
If you need a DAC that can drive line-level analog output (for example to a different device), and also a headphone amp, the JDS Element does the job.

The Element has analog RCA line-level output jacks, which the Jazz lacks. The Element also has unbalanced analog RCA input jacks which bypass the DAC and make it a simple analog headphone amp. This makes Element quite flexible as a line-level DAC, an analog headphone amp, or both together. When turned off, the DAC is still on and it routes the USB input to the analog RCA outputs. So you can use the Element as a DAC with line output, and as a headphone amp, leaving both plugged in at the same time. However, it will only drive one or the other, depending on whether it’s turned on. Put differently, think of the Element as “always on” for DAC, line input and output, and its power switch controls the headphone amp.

The Jazz is nothing more than a pure analog headphone amp. It has no analog RCA outputs to drive another analog line level device, nor can this be done from the headphone jack! That’s because of the Jazz’s active balanced ground drive. Line level unbalanced analog inputs assume the entire signal is on the + output, and signal ground is dead zero frame ground–that’s how unbalanced works. The Jazz emits a signal on the ground, which if passed to an unbalanced analog input, would be shunted to ground without any resistor. This makes the Jazz attempt to drive a 0-ohm load, which can blow the fuse or damage the amp. Use the Jazz only to drive headphones — not other audio components!

Volume: Advantage: Corda Jazz
The Element has an analog potentiometer volume control. It’s smooth, wide range, well balanced, but still a pot. The Jazz uses a stepped attenuator triggered by an analog pot; there is no pot in the signal path, only metal film resistors. It has about 30 steps, each about 1.5 dB apart. One can argue whether a stepped attenuator makes any audible improvement, but there’s no question the stepped attenuator is a superior design: cleaner signal with perfect channel balance at all volumes, and unheard of at this price.

Imagery: Advantage: Corda Jazz
The Jazz has a mode to artificially create a more natural stereo image from normal (non-binaural) stereo recordings. It’s a switch that blends channels with phase delay depending on the difference in L / R channels. I’ve used these before and they’re usually gimmicky. Meier’s is not a gimmick. It’s the only one I’ve heard that improves the image while getting out of the way of the music being otherwise sonically neutral or nearly transparent. I said “nearly” transparent. It does make the tone a tad less rich, a small emphasis in the mids to treble. I usually leave it off, except on recordings with extreme L-R separation, where for example a singer or instrument is entirely in one channel or the other. These are hard to listen to on headphones, and this switch fixes that.

Signal Isolation: Advantage Corda Jazz
Both amps have unbalanced analog output to the headphones. But the Jazz adds a twist: active balanced ground driving. Signal ground to the headphone is not the 0V frame ground that it would be with standard unbalanced. Signal ground contains some of the L and R signal combined, such that the net signal at each speaker of the headphone (difference between + and -) sums to pure L or pure R. Because the ground contains some L and R signal, the net field around the cable is near zero (not exactly zero, as it is with balanced). This isolates the signal better, immunizing it to hum or other electrical interference. Some might say this also makes the load easier for the power supply to drive, but the power supply is already over-engineered with its 10 W toroidal transformer.

Build Quality: Advantage Corda Jazz
Both have great build quality, but the Jazz is a small step higher both inside and out: the case, switches, knob, power supply and other internal components. The Element is by no means cheaply made, it’s a pleasure to view and handle. But the Jazz is a step up.

Sound Quality – Subjective Listening

Both sound great: clean, neutral, detailed and fast without brightness, deep bass without being bass-heavy. Both are dead silent even at high gain full volume – no hum or other background noise. Both have excellent measurements comparable to professional reference gear. Not having a DAC, the quality of the Jazz depends on the source. I compared the Jazz & Element using an Asus Xonar DX sound card to drive the Jazz, and driving the Element with a USB bit stream. I used Audeze LCD-2 headphones and extremely high quality recordings of a variety of music, mostly acoustic.

In this configuration, I preferred Jazz in overall sound quality, which countered my expectations since good solid state amps are so hard to differentiate in blind listening tests. The Jazz has the same level of clarity and detail as the Element, yet at the same time sounds slightly more rich in the bass and sweet in the mids and treble. Call it more musical, yet without any loss of neutrality or clarity. I emphasized the word slightly because the difference is subtle. Upon first impression they sound identical, though I feel well trained experienced listeners using excellent recordings would detect the difference consistently with careful listening in an ideal quiet environment.

That said, if I needed the flexibility that the Element provides–listening to music from a laptop where I must stream bits over USB because I can’t install a high quality sound card, or I needed a DAC with line level RCA output in addition to a great headphone amp, or I was using great but less than reference quality headphones like Sennheiser HD-600 instead of the Audeze–I would grab the Element in a heartbeat. To put some meat to that statement, my Element is not for sale.

By comparison, the Oppo HA-1 is the best of both worlds and more. Its analog amp equals or exceeds the Jazz, which is a high bar. Its Sabre ES9018 DAC is fantastic and has coax, toslink and USB inputs. It is fully balanced with both line level and headphone outputs, yet also has a single-ended outputs. It also has great flexibility with numerous inputs and outputs. The only feature it lacks is the Meier’s headphone image circuit, but I only miss it on those rare recordings with artificially extreme L-R separation. But the HA-1 is big and bulky, weighs about 15 lbs, costs 3x the price of the Jazz or Element and is no longer made.

Audio EQ Settings

Since I went to the dark side, and started using gentle parametric EQ to correct the FR of headphones & speakers to neutral, I want to collect the EQ settings here. My general philosophy is to make subtle corrections. FR response deviations are often related to other forms of distortion like phase or ringing. Amplitude corrections big enough to restore completely flat response can exacerbate those other factors. Thus I stick to subtle, gentle corrections that improve neutrality yet preserve the original character of the sound, short of restoring perfectly flat response.

When boosting levels, remember to apply a reduction in overall gain to avoid clipping. Take the biggest amplitude boost at any frequency and cut by that amount. This is in the voltage (not power) domain, so dB = 20 * log(V1/V2).

For example, if you apply +2.5 dB @ 4.5 kHz, then you must reduce overall gain by 2.5 dB, which is a gain ratio of 1 / (10^(2.5/20)) = 74.98%. Or just use 74%. When it comes to gain ratio, to avoid clipping, lower is safer. So always round down (truncate the decimal), not up.

Sennheiser HD-580

Characteristic FR: flat down to 50Hz, then roll off bass at about 6 dB per octave. Gentle dip of about 5 dB between 3500 and 9000 Hz. Narrower dip of about 6 dB between 10 and 17 kHz.

Parametric EQ Correction:

  • +4 dB @ 25 Hz, Q=0.67 (2 octaves wide — 1 each side)
  • +4 dB @ 14 kHz, Q=1.3 (slightly under 1 octave wide)
  • Gain: -4 dB = 0.63 = 63%

Subjective Difference:

This simple EQ transforms the venerable HD-580 making it more open, natural and neutral. Deep bass extension without impacting mid-bass and linearity. Slightly crisper transients and “air”. Even though the midrange is untouched, it sounds a touch more open, less boxy.

Audeze LCD-2

Characteristic FR: flat from zero to about 2 kHz. Gentle dip of about 7 dB between 2k and 9k. Flat from 9k on up.

Parametric EQ Correction:

  • +2.5 dB @ 4500 Hz, Q=0.67 (2 octaves wide — 1 on each side)
  • Gain: -2.5 dB = 0.74 = 74%

Subjective Difference:

Normally the LCD-2 sounds perfectly natural, yet a touch soft like listening from the 5th instead of 1st row, and correspondingly soft on detail. This EQ brings the LCD-2 back to the 2nd row and restores some lost detail, but without affecting its near-perfect voicing. It transforms the LCD-2 into the perfect headphone!

The 2016 and later LCD-2 are a touch brighter and need less EQ. Say 2 dB for these, and 3 dB for the 2014 model. CSD plots show the LCD series headphone tends to ring or resonate around 4-5 kHz, which is the trough of their natural response curve, so you don’t want to boost this freq too much.

Magnepan 3.6/R

Characteristic FR: depends on the room. My listening room has floor-to-ceiling tube traps 2′ diameter in corners behind the listener and 4″ thick RPG acoustic foam on the wall behind the listener. This EQ is busier than the headphones, which is unavoidable with in-room speakers, though I still managed to keep the rates gentle.

Parametric EQ Correction:

  • +3 @ 32, Q=0.67 (2 octaves wide — 1 on each side)
  • -2 @ 90, Q=1.41 (1 octave wide)
  • +3 @ 240, Q=0.4 (1.5 octaves wide)
  • -2.5 @ 1000, Q=0.67 (2 octaves wide)
  • +3 @ 3000, Q=1.41 (1 octave wide)
  • Gain: -3 dB = 0.7 = 70%

Of these, the bold-faced ones correct anomalies inherent to this speaker. The rest are room corrections. That is, the Magnepan 3.6/R is a near-perfect speaker when set up properly in a good room, but it rolls off the low bass and has a gentle lift around 1 kHz. The other 3 settings are corrections to my room.

How to Shrink Virtualbox VDI Volumes In-Place

In my case, Ubuntu 16 is the host OS, Windows 7 is the guest OS, with Virtualbox 5.0.40.

Before starting, ensure your Virtualbox is a VDI file. VMDK files can’t be resized–though they’re useful for other reasons, being compatible with other virtualization software like VMWare.

First, run the guest OS. Defrag the drive. Defragging crams all the files together with contiguous unused space at the end of the drive instead of scattered around. Then run: sdelete c: -z. You must run this from a command prompt having admin privileges. This step writes zeros across the unused space, which is critical because VirtualBox can’t compact the VDI unless the free space is full of zeroes. The sdelete command takes a long time after reporting 100%, appears to be hung. Be patient and let it finish.

Now shut down the guest OS. From the host OS command line, run: vboxmanage modifyhd file.vdi compact. Here, file.vdi is your VDI file.

Your’e done. The VDI file will be smaller. It will grow automatically as you use more of the guest OS disk space.

Note: don’t use the guest Windows 7 OS file management to shrink the volume. The free space it creates can’t be compacted by VirtualBox.