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_stentOre // Bluetooth_earspeakers // english

Test Bluetooth in-ear headphones

Comparison ERATO Audio - Apollo 7 True Wireless Audio vs. BRAGI The Headphone

The Erato is small, fits well in the ear, has -- by bluetooth standards -- clean sound and lasts for about two and a half hours. Its advantage: each earbud is independent and can be paired without the other. This permits the owner to use one bud while the other is recharging in the docking case. Disadvantage: the Erato is of low sensitivity, ca. 100 db/mW.

The Bragi is more sensitive, perhaps 103-106 db/mW. It is rather bulky and does not fit well in the ear. It's sound is characterized by a distortion in the 1-2 kHz region which makes listening rather unpleasant, reminding of the awful piezo "speakers" used in hearing aids. Only one bud, the right one, is active. The other bud is a slave and works only if placed in the left ear when pairing. I don't know how long the battery lasts: I never succeeded making the Bragi work that long.

The sample I purchased does not work properly. If paired with a transmitter it crashes every time there is a strong impulse (noise). It needs about a quarter hour after crashing to recover before it can be restarted and paired. The factory service did neither provide an explanation of this problem nor an effective way to fix it.

Regrettably, the Bragi will be returned to vendor.


Speakers of the stentOre brand first appeared in Italy in the early 1980s.. They were built in a small series in San Lorenzo in Rome and are still used by their owners. They were — revolutionary for their time — dipole speakers with an open back and a separate subwoofer. Since then, technology has evolved. This blog aims at contributing to the discussion.

Of the difficulty of writing a technical blog & the pitfalls of medium-size languages

How lucky are those Dutch, Finns and Icelanders. To address a large audience they are forced to write in English -- and their fellow country men & women are accustomed to reading English prose if they wish to grasp what is going on in the world.

Less fortunate are those French, Russians, Germans, Italians and even Hispanics whose language is of medium size. Googling in this kind of language suggests to them that they can find satisfactory answers to most pressing questions. So why bother learning enough English to jump into the vast pond of international communication?

The mid-size languages constitute an intellectual trap. Pursuing a technical discussion in these languages is like catching fish in an aquarium.

While science, banking and business have long become accustomed to converse in English (and some universities have even abandoned the national language altogether), most techies and ordinary people are still monolingual. They may sport some degree of English literacy but not enough for conducting a meaningful exchange with the world outside their mother tongue bubble.

Speaking in practical terms, this unfortunate situation obliges a technical blogger to write a bilingual blog

-- one in English language and
-- one in the national language for a local audience which is still largely English-illiterate.

Surely, a way of handling this problem would be to translate. But who likes to translate? A stupid and tedious job that offends the creative spirit.

Having said this, there is no excuse anymore. Let's get going!

Redbook Revival

"Compact Disc Digital Audio is the standard format for audio compact discs. The standard is defined in the Red Book that contains the technical specifications for all CD formats. The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc Committee and ratified as IEC 60908. The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc Committee and ratified as IEC 60908." (wikipedia)

In recent years, dissatisfaction with the quality of CD sound has led to an increasing infatuation of the audio community with so called high-rez formats:

"There is no standard definition for what constitutes high-resolution audio, but it is generally used to describe audio signals with bandwidth and/or dynamic range greater than that of Compact Disc Digital Audio. This includes pulse-code modulation (PCM) encoded audio with sampling rates greater than 44100 Hz and with bit-depths greater than 16, or their equivalents using other encoding techniques such as pulse-density modulation (PDM)." (wikipedia)

Most of the few recent high-rez recordings are only available over the Internet, making the computer the main source of content for the audiophile. However, the high-rez sector covers only a minuscule part of the available recorded music (and not necessarily its best performances). The rest exists only in CD format which remains the standard of the music world. all the more since earlier experiments in high-rez formats -- the SACD and the DVD Audio -- sadly failed to gain market acceptance. Current efforts to launch DSD 128 are interesting but probably doomed to remain an audiophile niche market.

New efforts to squeeze more sonic value out of the CD format are therefore of prime importance. A look at current audio technology shows that the conversion from the digital format S/PDIF to analog format is the most critical aspect of CD reproduction. Hence, industry and do-it-yourselfers developed a plethora of D/A converters ("dacs") ranging from cigarette format to full shelf size and from a few $ to kilobuck monsters.

Not ignoring engineering achievements like the Polish Lampizator, the Canadian Auralic Vega and the American Benchmark DAC2 HGC, two approaches deserve special attention because they differ from the mainstream: the Japanese Korg DS-DAC 100 and the Canadian NAD M51.

The Korg is the first inexpensive DAC available which converts PCM in DSD 64 or 128 format. The advantage is that DSD does not require the infamous brickwall filter to remove the carrier frequency from the audio. A simple 12db filter suffices to eliminate the carrier. As a result, the Korg's CD reproduction is considered much more "liquid" and "analog" although in measurements, DSD does not appear superior to high-rez PCM. The Korg, of course, also accepts DSD input.

Unfortunately, the Korg is a pure USB DAC which means it accepts only recordings stored in a computer. There is no way to play a CD in the computer's onboard transport and listen to it in real-time in DSD. Consequently, there is also no S/PDIF input permitting to connect an outboard CD transport.

At about twice the price of the Korg there is the remarkable NAD M51. This heavy full size machine pursues the same goal as the Korg: to eliminate the brickwall filter. Whereas the Korg converts PCM in DSD, the NAD converts PCM to PWM, Pulse Width Modulation, the native format for DSD.

Contrary to the Korg, the NAD converts every incoming signal to PWM with a sampling rate of 844kHz controlled by a clock running at 108MHz. Its 35-bit architecture uses a similar PCM-to-PWM conversion as the NAD M2 amplifier.

As in the Korg, mild filtering suffices to eliminate the carrier frequency, with resultant sonic benefits. Contrary to the Korg, the NAD is a standalone unit and offers not only an USB input but S/PDIF and HDMI inputs as well. In addition, it sports a lossless digital remote volume control, remote toggling of inputs and a mute switch, making it a DAC/preamplifier. Being a standalone means the NAD is fully operational without computer support; only if the USB input is activated the computer needs to download a NAD custom application.

With its S/PDIF input the NAD accepts any signal between 16/24 and 24/192 which means that it tolerates digital processing inserted between the transport and the NAD. The processing can be effected by DSPs like the DEQX, the alluring Nanodigi or various DSPs from Behringer and other manufacturers. This means that digital room and speaker correction can be implemented before the NAD converts the signal to analog.

The result of this approach to CD reproduction is stupendous. Even if successful room and speaker correction has already lifted sound quality to remarkable levels, inserting the NAD M51 in lieu of a good modern DAC means achieving another level of clarity and precision.

No need here to describe the sonic virtues of the M51: John Atkinson did so in Stereophile. As usual, his review is stringent and deserves a "like".

Although the Redbook CD cannot claim high-rez qualities, it can come damn close if reproduced through an M51 and decent speakers or earphones -- both ideally electrostatic. With lesser transducers and without room/speaker correction you are likely to waste most of the virtues of the NAD M51.

Tuning Behringer

In addition to using an exceptional DAC like the M51, there is still another way of bringing the Redbook CD closer to hi-rez performance.

An American radio amateur aka Tyler KaoKa has developed a way of tuning the Behringer DEQ 2496 DEQ/DYN functions to deliver a perfect reproduction of a sinus wave.

eSSB Audio for the Radio Amateur Experimenter

Under the heading Behringer DEQ2496 Universal Critical Timing and DEQ Parameters

the site describes in detail a method to obtain correct Behringer DEQ 2496 DEQ/DYN timing parameters. It is useful to print out the recommendations and apply them precisely.

The result can be described as invigorating the CD sound. "Clean" and "lively" are the the attributes coming to mind. The tuning effort helps to move the speaker performance closer to the quality of the STAX earphones and their tube-powered amplifier. (Incidentally, with the STAX receiving its signal from the modest onboard DAC of the DEQ 2496 while the speakers are served by the NAD M51, the quality difference of the DACs reduces the sonic advantage of the earphones over the speakers.)

Tyler's work demonstrates that the Behringer DEQ 2496 is a sophisticated machine able to deliver more performance than most users realize.

(more to come -- pls watch this space)

© Heinrich v. Loesch


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