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Alt'F reviews the Broadcast Warehouse DIGILOG

08th April '99
Alt'F reviews the Broadcast Warehouse DIGILOG Stereo Coder kit - "KITHQSTEREO"

( Web Surf : Here is the complete text of a review that the famous french radio pirate Alt'F e-mailed me re: the recently released Broadcast Warehouse DIGILOG Stereo MPX kit. To contact Alt'F, look for clues on my site or go to the NG.)


Order, shipment:
Ordered by Internet, the Digilog cames two weeks after, by regular postal service.

BW has noticed me of a 10 days delay before shipment.

The digilog was well packed and protected for the transportation.


Documentation:
The Digilog comes with a manual. (Web : Thats like saying "Dr. Livingstone, I presume". I guess he really means "Wow, the 10 page documentation is very detailed and explains everything !!")

The product is well presented, and each functional section of the circuit and the underlaying technical choices are exposed and explained in details.

What an improvement over the old "filtered stereo coder" documentation !

I've did'nt assembled the Digilog, ( Web : meaning that he got the kit pre-assembled) but a look at the PCB and documentation shows it's very easy to assemble.


High quality black-oxyde PCB and parts:
The part's location are clearly indicated and all connections pins are labelled.

The connections pins are the same as those found on PC's motherboards, the connectors are very easy to find.

The parts quality is good, especially in sections where it's critical (metal film resistors, polyester capacitors in audio paths)


Features
Type: Digital switching stereo coder.

- Balanced audio inputs:
The Digilog has balanced audio inputs, you can use it with professional devices. Balanced system is much more immune against the hum and RFI than unbalanced system.

Note: you can operate the Digilog with unbalanced audio.

- 15KHz low-pass filter:
This filter prevents any audio frequency over 15KHz to interfere with pilot tone.

- Clipper:
Three modes are available. No clipping, whole band clipping, high-end clipping
Whole band: the clipper operates at all audio frequencies.
High-end: the clipper operates only on high frequencies.
You can use the high-end mode for clipping the peaks produced in the low-pass filter.

- Pre-emphasis:
Three mode are available. No pre-emphasis, 50µS and 75µS

- 19KHz pilot level:
Allows to adjust the pilot level

- L-R level:
Allows a fine adjustment of the L-R level.
An optimal L-R level brings optimal stereo separation for a particular receiver
(i.e. your hifi's tuner for home broadcasting applications)

- Stereo/Mono: Guess what ?!

- MPX out filter: cleans out any unwanted signal in the MPX signal


The ability to switch and adjust these features provides a way to experiment with different parameters and understand how
they affect the sound without changing parts. The included jumpers are very useful for fast with/without comparison.


Bells and whistles
The on-board split-rail power supply has output pins, providing a little -12/+12V source.

The 19 KHz pilot tone has 5V unbuffered output pins, useful for some RDS encoder.


Assembling and adjusting
Simply follow the instructions.

The Digilog can be fine-adjusted for optimum operation. The manual provides the essential informations for basic and fine adjustment methods.


Subjective audio impression
This is where things really begins !

After a basic adjustment, the first second of listening tells your ears that this stereo coder sounds very good (*3*)

The sound is clean, transparent, warm and natural.

The coder seems to "want" the modulation rather than being forced to "accept it".

The stereo separation is good, the center of the stereo image is cleary defined.

The treble are clean, the ringing in 15KHz low-pass filters is not noticeable with reasonnable modulation levels and high-end clipping.

In whole-band clipping mode, the peaks are effectively removed without alteration of the sound (Only if PEAKS are removed this way !!! Remember that a clipper is NOT a programme limiter NOR a compressor)

The noise level is noticeable, but totally acceptable (only my reference stereo encoder do better, the Digicoder is better than all other kits i know *2* )

Without knowing the bandwidth, s/n ratio and distortion, the sound seems very good, as good or even better in some situations than my reference stereo coder (*1*)


Conclusion
This is the stereo coder kit we've been waiting for a long time !

This coder is a real major improvement over other stereo coder kits, even the older "Broadcast Warehouse filtered stereo coder".

It's far better than Veronica's cristal stereo coder kit

The sound quality is impressive, the kit comes with all the features required for a clean broadcast (low-pass filters, pre-emphasis and clipper) even if you do not have an audio processing chain.

The switchables and adjustable features allows this coder to follow the evolution of your audio processing chain.

The clean MPX signal and low-distortion 19KHz pilot tone allows operation with RDS coders.

This coder makes the difference, especially with classical music and vocals which reveals the distortions.

Excellent for starting in the field of high-quality stereo.

Your ears will thank your wallet for the right-spent bucks !
(est-ce que ça se dit, ça, en Anglais ?)


Footnotes, references

*1* My reference stereo coder is a real professional AEV stereo coder

*2* Other stereo coder kits i've build/tested:
Veronica Cristal stereo coder kit
Boadcast Warehouse filtered stereo coder kit (now replaced by the Digilog)

*3* Test situation:


Audio sources:
CD Player, DAT Recorder PC with A/D D/A converters and related softwares
Tascam M216 16x4x2 console

Audio processing chain:
Two bands compression followed by two bands enhancer/exciter

Crossover: Behringer "Super-X" 4 channels, 2-ways crossover

High+Mid frequencies compressor/limiter: Behringer "Composer Pro" dynamics processor

Low frequencies compressor: Yamaha compressor/limiter

Enhancer/exciter/surround processor: Behringer "Ultrafex Pro"


Transmitters:
Veronica 1W PLL Kit, ref. "PLL"
DB Europe 20W (a real professional exciter)

Antenna: The tests were always performed on a dummy load, with 1W HF


Receiver, amp and speakers:
Consumer-grade "Vector Research" synthetized tuner
High-grade "Marantz" PLL tuner with modulation meter

Antenna: 300 Ohms inputs of the tuners shorted together by a 1-meter wire

Sansui AU-D7 DD/DC linear class A power amplifier with KLH loudspeakers

Alt'F , Avril '99

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13th Jan '99 : Visit Alt'F's site at http://www.compu.ch/dderbes/Altf/Index.htm (In French)

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