Categories: SECRETS Home Theater Q&A

EQ for Analog Inputs

Question:
I like using the automated EQ setup on my receivers. I also enjoy using the multi-channel audio outputs on my blu-ray player to take advantage of its DAC. But I’ve never found a receiver where the EQ will work with analog inputs. Why is that?

– John K
Portland, Oregon

Answer:
To have room correction active the signal must be in the digital domain. To do all 8 channels you would need eight 8 ADCs but modern AVRs have only 2 with limits process of analog signals to only stereo.

In the past AVRs included 6 ADCs to support the analog outputs of DVD players. This was important because the early AVRs did not support HDMI and early versions of HDMI did not support multichannel. Without the 6 ADCs connected to the 5.1 analog inputs, the only way to listen to multichannel was with the SPDIF connection which transmitted only compressed Dolby digital. Early HDMI was also plagued by green screens and muted audio. Analog audio and video connection provided a work around.

A long time has passed and all you will find in stores are Blu-ray players with robust HDMI outputs. Interoperability testing between components demanded by Best Buy among others has ended the green screen problem between Blu Ray players, AVR and TVs.

Today only, a few customers want to run analog outputs from a Blu-ray player to an AVR. It was thus easy for AVR designers to drop the added ADCs without anybody noticing about 5 years ago. Indeed, you will find most AVRs and even some Pre / Pros lack any multichannel input.

I should note that the stereo ADCs found in almost all multichannel products are not very good. You always want to connect with a digital cable if you are using room correction. Even if you are not using room correction it is better to go digital instead of direct mode. Designers assume analog stereo is being used only for legacy products like VCRS and cassette players. They reduce the cost of the analog input section, in addition to the ADCs as the struggle to add things like added DSP processing for ATMOS while keeping the total cost constant.

The only current product I know of with 6 ADCs is the Anthem D2v 3D and products designed for professional applications like the Datasat RS20i.

I should note that those multichannel ADCs on older products did provide a way to future proof a multichannel Pre / Pro or AVR. See the article below on how a reader has a modern home theater with an Anthem D1 which has no HDMI.

www.hometheaterhifi.com/technical/technical-reviews/don-t-let-the-upgrade-bug-bite-you-in-the-bum-be-happy-with-what-you-have-and-enjoy-the-music/

David A. Rich, Ph.D.

David A Rich received his MSEE from Columbia University and Ph.D. in Electrical Engineering from Polytechnic University of NYU. He specializes in analog and mixed-signal integrated circuit design, with a portfolio spanning from audio ICs for Air Force One to RF ICs for wireless cell phones. Holder of fourteen patents, David's industrial experience includes ten years at Bell Laboratories where he rose to Technical Manager. He has taught graduate and undergraduate courses in integrated electronics and electro-acoustics. David's interest in audio began very early under the influence of his father, who was a recording engineer during the halcyon days of RCA Records. He gained an early understanding of electronics building Echo, Heath, and Dynakits. At the start of quadraphonic sound, David was building decoders based on designs in Popular Electronics. During his teen years, he spent more time in the back of TVs than watching movies at the front of the set. He still has limited interest in things video. David has been a professional reviewer of audio equipment for more than two decades, serving as Technical Editor for The Audio Critic and Sensible Sound. He is a member of the Audio Engineering Society High-resolution Audio Technical Committee. Collecting classical recordings has been a passion that has run concurrently with involvement in audio hardware. David has a special interest in early- and mid-20th century American tonal composers. He is an avid fan of chamber music and leads the Selection Committee for the Bethlehem (Pennsylvania) Chamber Music Society Concert Series.