Integrex NRDC decoder

[Ianf]

I'd be interested to hear your impressions of Ambisonic decoding with the NRDC unit when you're able, and if you're able to A/B it against any other Ambisonic decoders, if you have any others.

I’ve a surround sound master SQ as well, so I’ll report back, though swapping all the connections is slow

 

[Soundfield]

I've often wondered if they were most common in the UK (but scarce elsewhere) because of the BBC's use of Ambisonics

No one ever bought any type of Ambisonic decoder to use it for decoding BBC Ambisonic transmissions. The BBC never broadcast anything encoded Ambisonically or publicly expressed any interest in doing so. They were interested in the performance of the Calrec soundfield microphone but only ever used it for stereo broadcasts.
As Richard Elen wrote in Studio Sound, October 1979-

"This year, the BBC took delivery of two Calrec Soundfield Mark III (production model) microphones. Prior to this, however, the BBC had already assessed the prototype Mark II mic - described by some as the most important mic development since Blumlein. It is perhaps unfortunate that the prototype Calrec soundfield mic didn't make its appearance on the BBC scene until after the first run of matrix-H and HJ experimental surround-sound broadcasts had been completed. It is hoped the transmissions in the latter format will start again soon, and will no doubt make use of the soundfield mic, but in the meantime, BBC studio managers and researchers are amassing a good deal of information on the performance of the mic in stereo applications, which will obviously be a great deal of use when surround broadcasts are continued."

But of course they never were continued. The public lack of interest in the whole year long quad experiment saw to that.

 

[Owen Smith]

But of course they never were continued. The public lack of interest in the whole year long quad experiment saw to that.

A large proportion of the UK public were still listening in mono on AM never mind FM or stereo. And of those listening in new fangled FM stereo, what proportion were interested in a surround format for which there were almost no decoders and definitely no decoders that performed well? (on HJ). It was doomed to failure before it even started.

 

[Ianf]

No one ever bought any type of Ambisonic decoder to use it for decoding BBC Ambisonic transmissions. The BBC never broadcast anything encoded Ambisonically or publicly expressed any interest in doing so. They were interested in the performance of the Calrec soundfield microphone but only ever used it for stereo broadcasts.
As Richard Elen wrote in Studio Sound, October 1979-

"This year, the BBC took delivery of two Calrec Soundfield Mark III (production model) microphones. Prior to this, however, the BBC had already assessed the prototype Mark II mic - described by some as the most important mic development since Blumlein. It is perhaps unfortunate that the prototype Calrec soundfield mic didn't make its appearance on the BBC scene until after the first run of matrix-H and HJ experimental surround-sound broadcasts had been completed. It is hoped the transmissions in the latter format will start again soon, and will no doubt make use of the soundfield mic, but in the meantime, BBC studio managers and researchers are amassing a good deal of information on the performance of the mic in stereo applications, which will obviously be a great deal of use when surround broadcasts are continued."

But of course they never were continued. The public lack of interest in the whole year long quad experiment saw to that.

This is very true, I had the original one and mainly used it for SQ, QS, as I had no access to B format at home, I did listen to some of the Alan Freemna

No one ever bought any type of Ambisonic decoder to use it for decoding BBC Ambisonic transmissions. The BBC never broadcast anything encoded Ambisonically or publicly expressed any interest in doing so. They were interested in the performance of the Calrec soundfield microphone but only ever used it for stereo broadcasts.
As Richard Elen wrote in Studio Sound, October 1979-

"This year, the BBC took delivery of two Calrec Soundfield Mark III (production model) microphones. Prior to this, however, the BBC had already assessed the prototype Mark II mic - described by some as the most important mic development since Blumlein. It is perhaps unfortunate that the prototype Calrec soundfield mic didn't make its appearance on the BBC scene until after the first run of matrix-H and HJ experimental surround-sound broadcasts had been completed. It is hoped the transmissions in the latter format will start again soon, and will no doubt make use of the soundfield mic, but in the meantime, BBC studio managers and researchers are amassing a good deal of information on the performance of the mic in stereo applications, which will obviously be a great deal of use when surround broadcasts are continued."

But of course they never were continued. The public lack of interest in the whole year long quad experiment saw to that.

A large proportion of the UK public were still listening in mono on AM never mind FM or stereo. And of those listening in new fangled FM stereo, what proportion were interested in a surround format for which there were almost no decoders and definitely no decoders that performed well? (on HJ). It was doomed to failure before it even started.

 

[Ianf]

This is very true, I had the original one and mainly used it for SQ, QS, as I had no access to B format at home, I did listen to some of the Alan Freeman shows in HJ on Radio1, I used to have cassettes, of them but long since gone,

 

[surround.sound.enthusiast]

Thanks Soundfield and Owen Smith. Because I'm not particularly familiar with ambisonics and its predessors I always mucking up matrix H, matrix HJ, and UHJ. I'm always throwing them in the same category because of lineage. I've also obviously been mistaking that the BBC continued broadcast tests with UHJ. The fact that they didn't explains why ambisonic decoders appear to be uncommon the world over. Thanks for straightening me out. Now to see how long it sticks...

 

[Owen Smith]

Thanks Soundfield and Owen Smith. Because I'm not particularly familiar with ambisonics and its predessors I always mucking up matrix H, matrix HJ, and UHJ. I'm always throwing them in the same category because of lineage. I've also obviously been mistaking that the BBC continued broadcast tests with UHJ. The fact that they didn't explains why ambisonic decoders appear to be uncommon the world over. Thanks for straightening me out. Now to see how long it sticks...

The simple approach is to pretend that matrix H and HJ never existed. There is so little material available in them that they might as well have not existed.

 

[tryphon]

I built the original decoder using tight tolerance mil-spec components in the phase-shifting networks. I also upgraded the power supply and tried unsuccessfully to upgrade the op-amps, but could not get rid of high frequency feedback when using more advanced op-amps. I have been tempted to produce a few updated units for sale, with high slew rate op-amps. However, I don't think there's a market for such a system today. I have loads of Nimbus and Unicorh UHJ CDs and they do sound wonderful through this decoder. I also have the Onkyo amp that had the Ambisonics surround decoder built-in, but I feel that my INtegrex+ Hafler 220 power amps sound a lot better than the Onkyo. I love the very low phasiness of UHJ Ambisonics and I also love the way the Integrex decodes SQ and QS Quadraphonic records. The picture shows my home-built Integrex decoder.

 

[amco]

RE: ¨ using tight tolerance mil-spec components in the phase-shifting networks ¨
... but phase shifting of audio is such a Hit and Miss process, that tight tolerance components are really just wasted ?!?
The proof is in the pudding, not in the blue sky !

 

[Soundfield]

The proof is in the pudding

Why do people mangle that expression to the point that it makes no sense? There is no proof in a pudding, only in the eating thereof!

 

[amco]

 

[Sonik Wiz]

RE: ¨ using tight tolerance mil-spec components in the phase-shifting networks ¨
... but phase shifting of audio is such a Hit and Miss process, that tight tolerance components are really just wasted ?!?
The proof is in the pudding, not in the blue sky !

I'm perplexed why you would call phase shifting in audio hit and miss. The phase shift desired can be predicted by simple math. In analog audio a phase shift circuit would most likely be a transistor with R/C components at the output. That resistor/capacitor pair has a time constant which can be translated into a frequency point & it's at that frequency there will be X deg phase shift as desired compared to the input signal.

Since phase shift is frequency dependent it will offer, say 90 deg phase shift at only one point. Multiple stages, or poles, are required to get close tolerance full audio bandwidth. One of the best examples demonstrating this is from an old Sansui patent regarding their QS encoding:

As you can see the overall phase shift goes from zero to almost 900 deg at the upper frequency but the phase difference is a pretty close 90 deg between the examined audio. In many block diagrams of this sort of stuff it doesn't mention that the zero deg signal is also phase shifted by a certain amount. Instead of zero deg phase shift it should be thought of as the phase shift reference. This shown in the diagram as outputs #43 & 46, which would be the front chs in a QS encoder. Output 44 lags 90 deg and output 46 leads 90 deg.

No mystery or hit and miss.

The Integrex decoder did it a bit better using IC's & phase shift in the feedback loop. This made for lower ripple & using a bi-polar power supply it eliminates the need for yet another coupling cap between phase shift stages.

The designers of the Integrex decoder used , as needed, odd values of R & C to get as close as possible to the theoretical phase shift points. I don't think MIL spec would help but precision components do & even Integrex knew that.

 

[Ianf]

I still love my NRDC and yes an electronic upgrade would be lovely, I’d certainly consider purchasing a unit using more modern components. But the Surround Sound Master V3 is pretty amazing

 

[Ianf]

Here is my setup

 

[tryphon]

Here is my setup View attachment 75705

Looks great!!!

 

[Sonik Wiz]

Here is my setup View attachment 75705

Hi Ian!

I notice in the pic both the Surround Master & Ambisonic decoder is set to SQ. What's your opinion of the strengths/weakness of the two units compared for SQ?

 

[Ianf]

Looks great!!!

So I tested both on the same SQ record, David Frost SQ Columbia Demo , and the Surround Sound Master is far more accurate at pinning the audio into place, that being said the NRDC is still pretty good after all these years
The modern DSP in the Involve unit does a better job