Updated: July 27, 2004
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Introduction | |||
![]() Why do you NEED an ABX/DBT tester? Well, it's the ultimate honesty tool. David Carlstrom describes it best on the ABX site:
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More information (external links, will open in new window) | |||
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Why yet another ABX/DBT machine? | |||
Software based testers such as PCABX will always put the PC in the signal path. With a good soundcard in the PC, this is not a bad thing an sich, but it is prohibitive for directly testing stand-alone equipment. For evaluating codecs or recordings that can be digitally transferred to the PC on the other hand, it's ideal.
In short:
Browsing the web I did not find many easy and good implementations. Also, the ones available are very expensive, with the cheapest one at $600. I thought I could do better and make a simple design, available for everyone to reproduce.
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How to keep the design simple... | |||
By buying off the shelf as much as you can! The hardware itself can be easy as pie.
![]() All you really need is:
Whilst searching for an easily driveable LC Display, I came across
Peter Anderson's serial LCD kit. Now this is easy, especially since there are also the
accompanying LCD and a series of
PICAXE microcontrollers available. This is a high-level, easy to
use microprocessor. I've been looking for a successor to the BASIC Stamps for use in tutoring undergraduate student
projects and this seemed a nice candidate. Also, the PICAXE bootstrap code has IR decoding for a Sony TV
remote implemented so I'd only need to connect a sensor, thus substantially shortening the programming
effort.
I used a spare
Odeion I board to mount the relays and power supply on (after all, this is almost a preamp...). In-
and outputs were hardwired to this board using silver cable from an old HP pulse geneator. The infrared
sensor is a
TSOP1738 that I removed from a scrapped project. It contains all preamplifiers and decoders and outputs
TTL. No hassle. The case used was acquired through dumpster diving (hence the extra hole, in which the
TSOP1738 was glued). As you can see, no expense has been spared. |
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Later... much later... | |||
![]() Finally, some spare time to connect the parts and write the software.
The microprocessor now contains a program that does the randomization of
the process and keeps the results hidden from the user. In this way you can perform a double blind test
on your own.
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The processor allow the user to switch when he/she feels like it, as often as desired (minimum session length = 2 seconds), until a decision has been made. The user writes down his decision and proceeds to the next session, or exits to the main menu to either switch back and forth between ABX and DBT, or to stop the testing and view the outcome.
![]() After a certain number of sessions (up to the user, with a maximum of 125), the results can be viewed. NOT before. Using P+ or P- one can scroll through the list, or by pressing 9 the list can be sent via RS232 to a PC.
![]() After viewing the results, there is NO way to go back to the sessions without wiping the memory. This effectively eliminates any chance of forehand knowledge of the session states.
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Software | |||
The code is released under the same
disclaimer as the schematics on this site.
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© UltrAnalog 2004 |