Hi All,
There was a discussion on the FB self help forum for Peugeot 1007 owners recently...
Someone said the standard radio fitted was mono Someone else said stereo,mono,stereo,mono....
After a while he clarified,?and said certainly the UK Models have CD Radios where the CD is stereo, but the tuner is mono.
Is this common?
Is it penny pinching?
Does it give a better S/N ratio?
???
TIA
Chris
Pass
Not very.
On FM, yes.
Stereo fm is far worse s/n to Mono FM. Many DAB stations are in mono whereas they are stereo on FM R4 extra and Smooth etc. I doubt anyone would fit a mono radio in a car these days, but there has for a long time been a progressive monoising circuit around that moves gradually to stereo as the signal level drops its supposed to be less annoying than the hiss from the stereo when itt is hanging on in bad areas. Its simply a mixer of the channels as the signal level drops below a set level. Some are frequency tailored as well. I think I'm right in saying the idea was invented by Phillips originally. However for DAB you need to ask Offcom not us. We will soon start this argument about restricting bit rates to cram more dross in at the expense of quality and the boiling mud mess you get on DAB over DAB plus. Brian
Since the module used these days has the features mentioned in my last post, I seriously doubt mono fm is supplied. Its more likely that dab is also in the car and the stations are in the main mono with some exceptions. Brian
Stereo car radios usually use stereo/mono blend on FM so as reception worsens the stereo effect is reduced rather than getting hissy. In a poor reception area the stereo FM would /sound/ mono which might be the cause of the confusion.
In a tin can like a Pug 1007, by the time you have got to 50mph you won't hear much detail from the radio anyway.
IIUC, for reasons of backward compatibility, a stereo FM transmission encodes stereo image into a pair of sum and difference signals[1]. So mono receivers can simply process the sum signal and get both channels combined into a single mono channel. A stereo receiver will need to add/subtract the difference signal from the main combined channel to get the separate L & R channels.
The sum signal is transmitted using FM and the difference signal is amplitude modulated onto a sub carrier shifted up from the main carrier. (IIRC there is also a pilot tone included just above the baseband audio to signal the received that its a stereo transmission). Since the AM modulation will suffer more in poor reception conditions it can also introduce hiss. Many radios hence include a Stereo/Mono switch to elect for mono with no hiss. Some of the posher car radios actually use a mixer for the stereo decoding, so they can switch the stereo in and out in gradual way depending on how much noise is being detected.
[1] Conceptually not unlike the way colour was added to mono TV
Not quite correct.
the reason for worsening S/N is quite simply that more bandwidth is needed to get stereo and that simply lets in more noise.
AM or FM doesn't really make much odds here.
..and actually appears to be a fairly close match to my overview above.
From your source...
"The (L+R) Main channel signal is transmitted as baseband audio limited to the range of 30 Hz to 15 kHz. The (L?R) signal is amplitude modulated onto a 38 kHz double-sideband suppressed-carrier (DSB-SC) signal occupying the baseband range of 23 to 53 kHz."
later:
"for a given RF level at the receiver, the signal-to-noise ratio and multipath distortion for the stereo signal will be worse than for the mono receiver."
Its the AM modulated difference signal (i.e. the bit that carries the stereo information) that suffers the poorer SNR. Whether one argues that is because or its modulation technique or its the lower bandwidth is a bit moot (I would say both are a factor, but AM is still the better choice for narrowband applications).
However I will concede a better wording may have been "Since its the AM modulated part of the signal that will suffer more in poor reception conditions..."
No, that still doesn't wash.
Its the 38kHhz subcarrier part that suffers worse. The FM S/N is only better because it occupies a humongous bandwidth -
400kHz - channel. Narrow band FM is just as noisy as AMThe stereo subcarrier is only 38khz wide.
AM is restricted to eseentially a channel as wide as the audio bandwidth being transmitted. FM may *or may not* use a wider channel,
That's why it's possible to get lower S/N.
The key thing is that its lower bandwidth.
>Thanks Brian,
but I think DAB (Digital And Bad??) Was just a twinkle when these cars and their factory fit radios were on the drawing board.
Cheers
Chris
I'd be surprised if they'd bother.
Car FM radios usually have a special stereo decoder. It notches out any interference pulses from the audio, and does a gradual blend from stereo to mono, depending of signal strength. Without that, FM reception would sound pretty nasty in all but the highest signal strength areas.
Think it costs the broadcaster more, the higher bitrate.
I have DAB in the old car - with a very posh and expensive aerial. Never ever heard boiling mud on that anywhere in the country. But it will change to FM if it loses the DAB signal totally.
DAB in the UK , testing from 1990 public rollout from 1995.
Peugot 1007 introduced 2005.
GH
In article snipped-for-privacy@davenoise.co.uk>, Dave Plowman (News) snipped-for-privacy@davenoise.co.uk> scribeth thus
Yep sure does, for a local sort of station DAB at say 32 odd K/bits around £40 K "ish" 128 around £70K and 192K forget it;(..
FWIW i had a new type of specialist FM receiver on demo/evaluation recently its a BW Broadcast encore series rebroadcast receiver which apart from being very good at what it does has lots of other needed bells and whistles like diversity reception, two tuner and multipath cancellation the capability to receive distant stations whilst ones on the same mast where it is may be knocking out kilowatts on close by channels on FM, DAB or TV etc.
However its main purpose is to pick up a distant transmitter and provide a high quality signal for local rebroadcast transmission.
Now its getting quite fashionable to use digital signal processing in such devices, they do now regenerate the 19K stereo pilot tone, regen the RDS etc but i had this one and put it on, you do have the Read the bloody manual to get it to do what you want it to do, but i had it tuned to a very good quality FM transmission pair of phones plugged in and just a few inches of wire plugged in the back as a makeshift aerial.
Went and had tea and came back, phones on very impressive audio, sounded very close to CD very quiet background all fine.
Further investigation revealed that what they call FMSI was enabled this is where the incoming difference signal is sampled out of band and a few other interesting things happen to it. Now they do have a measurement mode where you can listen to the original signal to check that under "as is" conditions when that was enabled the Almost CD quality disappeared in a very mushy hiss!
Hooking it up to a better aerial alleviated that but it was very interesting to see or hear rather just how good the signal processing was you can select conventional stereo "blend", well a slightly more advanced version etc, but switching the signal processing in the difference was remarkable even back on the bit of wire aerial.
At the prices these are its not intended as a domestic product and is a PITA to tune in different channels etc but just shows what can be done in the receiver to improve a deficiency of the original GE Zenith pilot tone system!..
So I've spent 24 years avoiding it :)
Last two cars came with DAB (whether you wanted it or not). Every motorway journey I did (Birmingham to Stoke, Eastleigh, Gloucester or Bournemouth, depending on the meeting) it cut out and "went funny". While FM was rock solid, as was the USB port for memory stick :)
Of course it's going to depend on where you are in the country. Same as any reception. City centres with tall buildings - or hilly country tend to show up the shortcomings of FM. And DAB was designed for mobile reception.
Which is why I was careful to state it was *driving* that I experienced shit performance. Driving across the vast mountain ranges of Worcestershire, Gloucestershire, Wiltshire, Hampshire and Dorset. All terrain that FM was crystal clear over. Except for a dead spot near M5J5 which I think was due to the sodding great transmitter there.
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