Joe's Dark Secret.

[Aerodyne]

This is a facinating topic. Sadly I can't think of much to add except to say that in the early 1960s I built a 'high fidelity' AM tuner, based upon a design in Practical Wireless. This thing used an EF50 and, I believe, an EF80. THe sound when played through my homebuilt stereo outfit was mono, of course - but quite remarkably detailed and pure from the BBC's stations, both medium and long wave. Fair enough, AM cannot have the dynamic range of FM but apart from that slight drawback, the thing sounded fantastic. This leads me to realise that AM truly has been 'nobbled'.
I too already miss watching the last night of the proms whilst listening to FM stereo. It was a great experience and one I miss. Preferring the audio to the visual, I now choose to listen and forget the enticing images!
-Tony

[Joe]

I miss being able to listen to the Light Programme on two wirelesses as the signals are no longer in sync. As I said in my original post my FM reception leaves something to be desired so if I put it on on my DAB while pottering about it gets very confusing to walk into a room with a conventional radio playing the same thing. I believe that Classic FM get 'round this by delaying the FM signal. I've also noticed that the DAB radio signal is also out of sync with that broadcast via digital television.

Ironically that Bush personal DAB radio has got a very good FM tuner built in so this isn't the problem it could be.

- Joe

[Mark Hennessy]

The human ear can filter out most things. But it is an Analogue device. So Analogue problems can be effectively ignored by the human ear and, if unlike me you have one, the human brain.

This is an attractive analogy, but I would argue that it varies enormously from person to person - too much to make it a valid assertion.

For example, I notice the clicks and pops from vinyl, and find them hard to ignore. I am also bothered by the HF distortion that you get from anything other than pristine vinyl, which of course gets worse towards the end of the side. Similarly, I am bothered by FM multipath distortion. I confess I am listening to DAB at the moment (Absolute 80s at 112kb/s), and despite the low bit rate, what bothers me at this moment is the excessive (dynamic range) compression pumping away in sympathy with the beat and stealing the life from the performances - which is an analogue distortion, even if modern processors are implemented in DSP.

With CD, I know that any audible problems such as distortion or a general "hardness" to the sound are caused by the recording or mastering process - not the medium. As previously discussed, my vinyl copy might sound "nicer", notwithstanding the "analogue distortions" mentioned above, because it's been mastered differently.

I might not enjoy certain CDs because of this, but at least I know that I haven't got to get the microscope out to check and clean the stylus, then double-check the tracking weight, cartridge alignment in the headshell and the vertical tracking angle. Similarly, if a CD sounds a little lacking in HF, I know that I haven't got to find the oscilloscope and test cassette and double-check the azimuth. The worst-case scenario might be a skipping CD, although I can't remember the last time I heard one of these on my system; I handle all my CDs with the same care as vinyl. That said, many audio enthusiasts (I refuse to use the term "audiophile") enjoy this constant worrying and tinkering and regard it as part of the process - a bit of a Protestant work ethic perhaps...

For the sake of balance, whenever I listen to good vinyl, I spend most of the time in wonder - thinking things like "this has no right to sound this good"! And on a slightly different level, I recently picked up a Bush SRP51 from eBay for pennies - I had one of these as a kid, and thought it would be interesting to see how I started my audio journey some 30+ years ago. I have to say that it sounds amazingly good given the technology - and particularly enjoy the bass from the Sonotone cartridge, which is amazingly entertaining. It's not accurate or neutral, but it's fun! The kids play their 7" single collection from the 1970s and 80s - and will probably hate me for it when they're teenagers! Interestingly, the Garrad 2025TC is unable to reliably track the bass in the break of "Hit Me With Your Rhythm Stick", despite the ruinously high tracking force, though my hi-fi decks have no problems. I refer you to a previous post regarding vinyl mastering...

My turn to generalise: essentially, we as creatures like our audio with a little bit of distortion provided it's even-order harmonics that don't extend too far (we hate odd harmonics, and the higher they extend, the worse they are). Odd harmonics are generally caused by clipping and crossover distortion, and even harmonics are caused by the gentle compression of analogue mediums like tape, vinyl and radio broadcasts. A good 1/4" tape machine would produce ~3% distortion at maximum mod when well lined up, yet it sounded just fine back in the day. Whereas just 1% crossover distortion is horrible to even the most uncritical ear - partly, of course, because it's always there whatever the level

I also wonder if it's what we've got used to? I got my first CD player when I was 16 so have perhaps been used to "digital sound" for a greater proportion of my life than others on here (not wishing to offend anyone, of course ). Also, I notice that I'm more critical of HF than many of my older friends and colleagues - indeed I'm still bothered by line whistle, although these days I regard that more as reassurance than a nuisance. I could name a certain brand of speakers sold as "monitors" that have their treble tilted up by about 10dB above 8-10kHz, and they literally hurt me, but my older colleagues quite like them. Go figure...

I also don't claim to have a human brain

Mark

[Mark Hennessy]

This is a facinating topic. Sadly I can't think of much to add except to say that in the early 1960s I built a 'high fidelity' AM tuner, based upon a design in Practical Wireless. This thing used an EF50 and, I believe, an EF80. THe sound when played through my homebuilt stereo outfit was mono, of course - but quite remarkably detailed and pure from the BBC's stations, both medium and long wave. Fair enough, AM cannot have the dynamic range of FM but apart from that slight drawback, the thing sounded fantastic. This leads me to realise that AM truly has been 'nobbled'.

Well, AM is just about OK for television :P

The only problem with using AM for audio is AGC, which of course means you have a compressor in your radio. Of course, with video, you can derive the AGC from the sync pulses...

I'm looking forward to eventually reinstating my workshop, and one of my first projects will be an AM transmitter

And digital delivery certainly does screw up simulcasting. Not surprising, given that it seems to be hard enough to keep an audio stream in sync with the pictures with a TV service!

Joe, you're right about Classic FM. A while back I found an interesting document about their broadcast infrastructure: http://www.ibs.org.uk/files/04_Clasic_FM_Relocates.pdf

Mark

[Aerodyne]

No AGC with the aforementioned TRF hi-fi tuner design, Mark. In any case, surely the delay in AGC would limit it's ability to compress?
I enjoyed reading the Classic FM link.
-Tony

[Aerodyne]

Ignore the bit about delay limiting compression. My mistake - I realised as soon as I uploaded it!
-Tony

[BG405]

I have a DAB radio too, a decent Roberts set and to be honest I'm appalled by the poor coverage, the signal is absolute rubbish and here in Leicester we only get one (yes just 1!) multiplex compared to Nottingham's 3, so no BBC or local services, just the commercial MUX. I wouldn't recommend it to anyone here


Brian