PC4uMusic & a head-related transfer functions

 

The entries on this blog cover various topics that may seem unrelated, but they have a common denominator. It's about a head-related transfer function (HRTF) is a response that characterizes how an ear receives a sound from a point in space. Microsoft has been working on this topic for years and in their presentation you can read, among others:

Head-related transfer functions

The temporal and spectral cues used by our auditory system to determine the direction of arrival of a sound source can be expressed in head-related transfer functions (HRTFs). HRTFs are measurements that capture the directivity patterns of human ears, that is, the way sound, arriving from a certain direction, reaches the left and right ear. HRTFs are a function of source azimuth and elevation, distance, and frequency.  

In PC4uMusic configurations, this applies especially to practical applications with the Microsoft system driver for the sound processor built into the motherboards. 

They have been optimally set to work with the free AIMP program to drive 4 speakers with an analog signal converted from digital with 32-bit float precision at a frequency of 192 kHz. However, it turns out that the possibilities are even wider.

There is already a spiral audio plugin for foobar2000, which is not technically perfect, but points in a direction with impressive potential.   It is an alternative to plugins that allow this program to work with Windows Audio Session Application Programming Interface (WASAPI) or Audio Stream Input/Output (ASIO).

  

Automatic Room Calibration (Correction) was used for testing with AIMP and foobar2000. It is available in the Microsoft driver. It is very useful for faithful music reproduction at home with 4 speakers

Practical comparative tests were carried out, among others: with analog solutions for quadraphony in the Sansui QS-1 decoder, which is mentioned in Wikipedia:

In 1971, Sansui introduced the Quadphonic Synthesizer QS-1, which could make simulated four-channel stereo from two-channel sources. Sansui developed the QS Regular Matrix system, which made it possible to transmit four-channel Quadraphonic sound from a standard LP. The channel separation was only 3 dB, but because of the human way of hearing it sounded relatively good. In 1973, Sansui introduced the more advanced QS Vario Matrix decoder with 20 dB separation.

Wikipedia also states: SQ records could give some amount of quadraphonic effect when played through a QS Regular Matrix decoder, although only accurately decoded playback is via a correctly designed SQ decoder.  

However, it was the calibration of loudspeaker placement that was the biggest problem from the very beginning, but there was little awareness of it because there was no appropriate digital technology at the time. As a result, other solutions with analog technology were sought and there is also information about them in Wikipedia: The early SQ decoders could not produce more than 3 dB of separation from front to back. Early "Front-rear logic" circuits were introduced to enhance separation to 12 dB and later "Full logic" circuits 20 dB, but both provided poor performance, very noticeable gain-pumping and an unstable 'swaying' sound field.

An interesting feature here is also the analog solution for playing binaurally recorded music through speakers. Japan Victor Company (JVC) offered them under the name Biphonics. The flagship product was BN-5, which was mentioned, among others, in the text entitled: Ambiophony and Rendezvous on SR2 with Roger Moor. 

 The JVC HM200E, which was often advertised together with the BN-5, is a unique headset where the built-in microphones have untapped measurement potential for calibrating 4 speakers placed in a room.

Even with the most reputable equipment, measurements are taken with one microphone, and we have two ears. This must be taken into account, because the most important thing is what we want to measure to ensure faithful music reproduction. The quality of the microphone is of course important here, but it is most important for laboratory measurements in soundproofed chambers to create curves for advertising materials of loudspeaker manufacturers.

MathAudio Room EQ is a professional program for studio use, but there is also a free version for foobar2000. It even has a measurement function with left and right microphones, but there is no way to implement this in practice