Monthly Archives: November 2015

audio – Why aren’t active headphones equalized to a flat frequency response? – Electrical Engineering Stack Exchange

Of all the components in the electroacoustic transmission chain, headphones are the most controversial. High fidelity in its true sense, involving not only timbre but also spatial localization, is associated more with loudspeaker stereophony due to the well-known in-head localization of headphones. And yet binaural recordings with a dummy head, which are the most promising for true-to-life high fidelity, are destined for headphone reproduction. Even in their heyday they found no place in routine recording and broadcasting. At that time the causes were unreliable frontal localization, incompatibility with loudspeaker reproduction, as well as their tendency to be unaesthetic. Since digital signal processing (DSP) can filter routinely using binaural head-related transfer functions, HRTF, dummy heads are no longer needed.


Still the most common application of headphones is to feed them with stereo signals originally intended for loudspeakers. This raises the question of the ideal frequency response. For other devices in the transmission chain (Fig. 14.1), such as microphones, amplifiers and loudspeakers, a flat response is usually the design objective, with easily definable departures from this response in special cases. A loudspeaker is required to produce a flat SPL response at a distance of typically 1 m. The free-field SPL at this point reproduces the SPL at the microphone location in the sound field of, say, a concert being recorded. Listening to the recording in front of a LS, the head of the listener distorts the SPL linearly by diffraction. His ear signals no longer show a flat response. However, this need not concern the loudspeaker manufacturer, since this would also have happened if the listener had been present at the live performance. On the other hand, the headphone manufacturer is directly concerned with producing these ear signals. The requirements laid down in the standards have led to the free field calibrated headphone, whose frequency response replicates the ear signals for a loudspeaker in front, as well as the diffuse field calibration, in which the aim is to replicate the SPL in the ear of a listener for sound impinging from all directions. It is assumed that many loudspeakers have incoherent sources each with a flat voltage response.


I was introduced to the whole concept of remixes via an album of just Depeche Mode – Behind The Wheel tracks. An outstanding memory from  my life is of driving home with a friend from college, six hours from Pittsburgh to New Jersey, the two of us listening to one outstanding mix of Drive after another, the same song but a different experience with each, perfect for a very long , straight drive through the night.

We were sober and awake, focused on the single-minded task of getting home safe at 85 miles per hour and without speeding tickets. Drive, the music, became a recitation, repeated. A mystic will  use repeated recitation of a religious text to achieve a transcendent state. To hear the voice of God. And so it was with the music on us.  The beats felt like tires as they pushed off the road. Measures replaced miles. A rhythm set in. A trip once laborious became transcendent.

And then came that moment. One of the mixes included a piano riff that was at once both solid and over the top. It came from under an accompaniment, edged its way into the foreground, and found itself center stage.

Like an actor with her last chance of making it big,  it quickly worked though its perfunctory skills. Practiced stepworks and trills were presented. And then presented again, only repeated to top the earlier round. Modulation to keep the audience’s full attention, and then once more and again, to the point where it was twirling around and over itself to the point of dizziness.

When it decided to end, the end was abrupt, to make you acutely aware of its absence. My friend and I took a shocked look toward each other and broke out laughing, an shared acknowledgement of the spontaneity, fun, and utter brilliance of it.

Things get lost and I lost the cassette. Over the years I’ve  thought back to that ride, that Drive, that perfect moment.


Still looking for that mix, but I’m starting with this:

Depeche Mode Behind The Wheel Beatmasters Mix – Mp3 Download – Song Uncle

Holomorphic Functions

In mathematics, holomorphic functions are the central objects of study in complex analysis. A holomorphic function is a complex-valued function of one or more complex variables that is complex differentiable in a neighborhood of every point in its domain. The existence of a complex derivative in a neighborhood is a very strong condition, for it implies that any holomorphic function is actually infinitely differentiable and equal to its own Taylor series.


Holomorphic functions are also sometimes referred to as regular functions[2] or as conformal maps. A holomorphic function whose domain is the whole complex plane is called an entire function. The phrase “holomorphic at a point z0” means not just differentiable at z0, but differentiable everywhere within some neighborhood of z0 in the complex plane.


The foundation of all location-based apps and services is the ability to determine where the user is located. Then, for applications such as navigation and augmented reality, direction of travel or the direction the user is facing are vital pieces of information as well.