Recording - December 2010 - 46

BY DAVE MARTIN

Avenson Audio IsoDI
An exceptional DI offers some neat tricks

Avenson Audio is a Texas-based company that makes handy tools that sound great and are often overlooked by bigger players in the audio field; Avenson’s Small DI (reviewed June 2006), for example, is a transformerless phantom-powered DI that can fit into any pocket or pouch, while the STO-2 is a matched pair of omnidirectional microphones at a reasonable price. Avenson even makes a reference-quality headphone amplifier with an interesting crossfeed circuit that intentionally reduces the extreme separation that headphones can exhibit. But today’s discussion is about the Avenson Audio IsoDI—yet another handy problem-solving tool at a fairly reasonable price. What’s a DI? This might seem a silly question, but from time to time it’s worth revisiting the basic premises of the technology we use. Depending on who you ask, “DI” is an acronym for “Direct Injection”, “Direct Input”, “Direct Interface” or “DI Box” (the last by those who don’t really understand acronyms). At the most basic level, a DI has two primary functions: First, it is an impedance-matching device and second, it provides a balanced output suitable for long cable runs.
46
RECORDING DECEMBER 2010

In the days when tubes ruled the earth, the input and output impedances of electronic devices were designed to match—usually at 600 Ohms. When the output and input impedances match, the maximum amount of power is transferred from the output of one device to the input of the next device in the chain. When the impedance of the input is at least 10 times that of the source, the result is called “bridging”, which results in the maximum voltage transferred between the source and the input. Effectively, this means that the output impedance of a given device is much lower than the input impedance of the device it’s being plugged into. Most electronic devices these days are designed with bridging inputs. To bring this discussion back to DI boxes, the output impedance of a typical guitar or bass is quite high; simply plugging it into an amplifier with a lowimpedance input usually results in a lessthan-optimal sound, including distortion or a lack of low frequencies. A DI helps this situation by having an extremely high input impedance. For example, the input impedance of the Avenson IsoDI is 10MΩ (Ω is the symbol for Ohm) and the output impedance is 150Ω.

The other primary function of a DI, which is to balance the signal so that long cable runs don’t degrade the sound, can be done either with a transformer or with an amplifier stage. Though there are a couple of transformers in the unit, the IsoDI uses an amplifier stage for this purpose. This is part of what makes the Avenson IsoDI a most interesting box; it’s a phantom-powered DI that uses a transformerless FET design for the main signal path, but has both a transformer-isolated power supply (which allows for a ground lift while operating with phantom power) and a transformer-isolated output that can be used to isolate the unbalanced output. The details At first glance, the Avenson IsoDI is simply a clean, high-bandwidth DI, eminently usable for the variety of tasks one needs a DI for in live or recording situations. When a pair of the IsoDIs appeared in the studio here, they were immediately pressed into use on a variety of keyboard sessions (both synthesizers and classic



Table of Contents for the Digital Edition of Recording - December 2010

Recording - December 2010
Fade In
Contents
Talkback
Recording’s 2010 Holiday Gift Guide
Theme Music for TV—A Production Report
Royer Labs R-101 Ribbon Microphone
Recording SFX—A Career Option?
Primacoustic IsoTools
Avenson Audio IsoDI
Getting Your Music Heard In Today’sCommercial Culture
Preview: Yamaha AvantGrand
It’s Your Music—Know Your Rights.Chapter 9: Trademark Basics
Sonoma Wire Works GuitarJack Model 1and FourTrack 4.0.1
Readers' Tapes
Advertiser Index
Fade Out
Recording - December 2010 - Recording - December 2010
Recording - December 2010 - Cover2
Recording - December 2010 - 1
Recording - December 2010 - Fade In
Recording - December 2010 - 3
Recording - December 2010 - Contents
Recording - December 2010 - 5
Recording - December 2010 - Talkback
Recording - December 2010 - 7
Recording - December 2010 - Recording’s 2010 Holiday Gift Guide
Recording - December 2010 - 9
Recording - December 2010 - 10
Recording - December 2010 - 11
Recording - December 2010 - 12
Recording - December 2010 - 13
Recording - December 2010 - 14
Recording - December 2010 - 15
Recording - December 2010 - 16
Recording - December 2010 - 17
Recording - December 2010 - 18
Recording - December 2010 - 19
Recording - December 2010 - 20
Recording - December 2010 - 21
Recording - December 2010 - 22
Recording - December 2010 - 23
Recording - December 2010 - 24
Recording - December 2010 - 25
Recording - December 2010 - 26
Recording - December 2010 - 27
Recording - December 2010 - 28
Recording - December 2010 - 29
Recording - December 2010 - 30
Recording - December 2010 - 31
Recording - December 2010 - 32
Recording - December 2010 - 33
Recording - December 2010 - Theme Music for TV—A Production Report
Recording - December 2010 - 35
Recording - December 2010 - 36
Recording - December 2010 - 37
Recording - December 2010 - 38
Recording - December 2010 - 39
Recording - December 2010 - Royer Labs R-101 Ribbon Microphone
Recording - December 2010 - 41
Recording - December 2010 - Recording SFX—A Career Option?
Recording - December 2010 - 43
Recording - December 2010 - Primacoustic IsoTools
Recording - December 2010 - 45
Recording - December 2010 - Avenson Audio IsoDI
Recording - December 2010 - 47
Recording - December 2010 - Getting Your Music Heard In Today’sCommercial Culture
Recording - December 2010 - 49
Recording - December 2010 - 50
Recording - December 2010 - 51
Recording - December 2010 - 52
Recording - December 2010 - 53
Recording - December 2010 - 54
Recording - December 2010 - 55
Recording - December 2010 - Preview: Yamaha AvantGrand
Recording - December 2010 - 57
Recording - December 2010 - It’s Your Music—Know Your Rights.Chapter 9: Trademark Basics
Recording - December 2010 - 59
Recording - December 2010 - 60
Recording - December 2010 - 61
Recording - December 2010 - Sonoma Wire Works GuitarJack Model 1and FourTrack 4.0.1
Recording - December 2010 - 63
Recording - December 2010 - Readers' Tapes
Recording - December 2010 - Advertiser Index
Recording - December 2010 - 66
Recording - December 2010 - 67
Recording - December 2010 - 68
Recording - December 2010 - 69
Recording - December 2010 - 70
Recording - December 2010 - 71
Recording - December 2010 - Fade Out
Recording - December 2010 - Cover3
Recording - December 2010 - Cover4
http://www.nxtbook.com/musicmaker/musicmaker/recording_202003
http://www.nxtbook.com/musicmaker/musicmaker/recording_202002
http://www.nxtbook.com/musicmaker/musicmaker/recording_202001
http://www.nxtbook.com/musicmaker/musicmaker/recording_201912
http://www.nxtbook.com/musicmaker/musicmaker/recording_201911
http://www.nxtbook.com/musicmaker/musicmaker/recording_201910
http://www.nxtbook.com/musicmaker/musicmaker/recording_201909
http://www.nxtbook.com/musicmaker/musicmaker/recording_201908
http://www.nxtbook.com/musicmaker/musicmaker/recording_201907
http://www.nxtbook.com/musicmaker/musicmaker/recording_201906
http://www.nxtbook.com/musicmaker/musicmaker/recording_201905
http://www.nxtbook.com/musicmaker/musicmaker/recording_201904
http://www.nxtbook.com/musicmaker/musicmaker/recording_201903
http://www.nxtbook.com/musicmaker/musicmaker/recording_201902
http://www.nxtbook.com/musicmaker/musicmaker/recording_201901
http://www.nxtbook.com/musicmaker/musicmaker/recording_201812
http://www.nxtbook.com/musicmaker/musicmaker/recording_201811
http://www.nxtbook.com/musicmaker/musicmaker/recording_201810
http://www.nxtbook.com/musicmaker/musicmaker/recording_201809
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201808
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201807
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201806
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201805
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201804
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201803
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201802
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201801
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201712
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201711
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201710
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201709
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201708
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201707
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201706
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201705
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201704
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201703
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201702
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201701
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201612
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201611
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201610
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201609
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201608
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201607
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201606
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201605
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201604
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201603
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201602
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201601
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201512
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201511
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201510
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201509
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201508
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201507
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201506
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201505
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201504
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201503
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201502
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201501
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201412
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201411
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201410
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201409
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201408
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201407
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201406
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201405
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201404
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201403
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201402
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201401
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201312
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201311
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201310
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201309
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201308
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201307
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201306
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201305
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201304
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201303
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201302
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201301
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201212
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201211
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201210
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201209
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201208
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201207
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201206
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201205
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201204
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201203
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201202
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201201
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201112
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201111
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201110
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201109
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201108
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201107
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201106
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201105
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201104
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201103
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201102
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201101
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201012
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201011
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201010
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201009
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201008
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201007
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201006
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201005
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201004
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201003
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201002
http://www.nxtbook.com/nxtbooks/musicmaker/recording_201001
http://www.nxtbook.com/nxtbooks/musicmaker/recording_200912
http://www.nxtbook.com/nxtbooks/musicmaker/recording_200911
http://www.nxtbook.com/nxtbooks/musicmaker/recording_200910
http://www.nxtbook.com/nxtbooks/musicmaker/nxtd
http://www.nxtbookMEDIA.com