You said in a different thread about having trouble with the sounds in “wythnos yn ôl” and variants of that - I’m not sure what you mean by variants, do you mean other phrases with ‘wythnos’ in them, or other phrases with ‘yn ôl’ in them?
I’m guessing that possibly the bit causing concern is the ‘wyth’ syllable? The trick to getting the hang of this is imagine you are yelling at a bully… “Oi thug”
Then drop the ug to leave “oi th” - that’s your ‘wyth’!
Also in the other thread, it was asked “What, if anything, is the secret of the LL?” (especially when it appears in the middle or end of a word)
I’ll repost my answer here for those who might find it useful and won’t know to look in the other thread.
Try this -
Step 1: slowly say the normal L sound preceded by all the vowel sounds you can think of -
e.g. AL, ALL, ELL, ILL, OL, OOL, ULL…
and pay attention to where your tongue is position everytime you make the L sound.
Step 2:
Now, repeat all those but this time, instead of making the L sound, keep your tongue exactly where it is (i.e. about to make the L sound), but just blow, letting the air go either side of your tongue.
Keep doing this with these one syllable combinations eventually getting faster, then when you feel you’ve got the hang of it, practice it in actual Welsh words where the LL comes in the middle or the end, again saying them slowly to begin with then speeding up.
You’ll soon be able to do it without even thinking about it 
…and when you can say “a spoon and a knife” - “Llwy a chyllell” I doubt you’ll have trouble with any LL ever again! 
What a fantastic idea for a thread @siaronjames!
I was browsing the old forum recently and found this about pronouncing the ‘ll’ sound…
Touch the roof of your mouth (just behind your top teeth) with the tip of your tongue and blow gently in to the roof of your mouth. As you are blowing gently in the roof of your mouth the position of your tongue forces your outward breath through the sides of your mouth. The resulting sound shouldn’t be harsh but sound like more of a whisper or gentle gushing water. The key is don’t force it till you’re spitting… there should never be any spitting…
A good way to practice the sound is to take a deep breath, then slowly and gently let it out through your mouth, moving your tongue in and out of that position where its tip touches behind your top teeth. By doing this you go in and out of the ‘ll’ sound which makes it easier to hear how the sound is formed and how gentle it is. 
There shouldn’t be any ‘ck’ sound.
I think this is part of what confuses me the most: that people pronounce the LL in such different ways; and, like a lot of people learning another language, I’m mistakenly assuming there’s only one “real” way to say it. But I notice that your LL is quite soft, Aran’s is much sharper, while other people pronounce it… well… “harsh” is exactly the word. I’m possibly having trouble because I’ve been trying to go in the harsh direction and end up with a uncontrollably flapping tongue; but if I say it softly, as you do, I don’t have much trouble at all. I can even pronounce “Llwy a chyllell” without my tongue falling out of my mouth 
I suppose it’s just like the letter ‘R’ in that it can sound very different from person to person. I’ve even heard some people (Dai from Pobol y Cwm for one and maybe Tudur Owen too) ‘rolling’ the ‘LL’ sound which is quite something. As long as you’re understood I don’t think anyone would even comment.
Yes! I have a very difficult time trilling my “r” sound (which I know is not over-accentuated in all Welsh dialects). I could never do this for Spanish either. It feels like my tongue just isn’t limber enough. It gets stuck or goes limp instead of flapping. Is there any sort of exercise I could do to work on this?
Actually I’ve always had the same problem and my rolled r is still very much hit-and-miss so we’ll both have to wait for for someone else to post an exercise for that!
My wife (Glenda) and I think a bit like an English R, but push your tongue slightly against the pallet. So the tip goes up a bit and the mid part does down a bit. A bit like the LL but make an rrr sound and don’t move your tongue back ar open your mouth more as in the English Ra. So Short RR for a tapped R and longer for trilled rrrrrr 
Can you do the brum brum noise one would make when playing with toy cars? Silly question I know, but it’s the same thing in practice.
Rolling 'r’s is basically the tip of your tongue vibrating against the alveolar ridge on the roof of your mouth because of the air you force past it, along with a humming/vibrating noise from your throat/vocal chords.
It’s difficult to explain and is something which definitely comes with practice. I’ll see if I can find any links on the Internet…
OK, this seems to explain it quite well…
Not sure if she is doing N or S course. But Iestyn pronounces Wythnos Awthnos rather than Oithnos.
Ah, I see. That would explain it. Awthnos (awth as in author + noss) is just as correct as oithnos.
Some words do have regional variations, and the thing is every variation is correct. Where there are different ways of pronouncing a word, the best advice is to go with the one you remember or find easier to say (even if it doesn’t sound exactly like the one the person you are listening/speaking to is using) because as long as it’s one of the ways of pronouncing it correctly, it will never be wrong.
May I ask if you speak northern or southern Welsh Siaron?
I ask because I’ve often wondered if there is a subtle difference between the way these are pronounced between north and south.
I’m aware of the pronunciation that you convey in your excellent example above, but I’ve often thought I’ve heard it slightly differently from northern speakers (e.g. on Rownd a Rownd, e.g. in the word “hwyl”).
However, sometimes I’m convinced there is a basic difference, and at other times I’m convinced there isn’t! I realise that we are definitely in “paid a phoeni” territory here, but even so, since we are on this subject, I’d be interested in opinions.
Well the answer isn’t quite as simple as North or South, I’m afraid. I use Northern forms, as the bulk of my Welsh speaking has been here in the North (so I say isio rather than eisiau or moyn, mae gen i rather than mae gyda fi, and fo rather than fe, for example), but I started learning while I was still in the South and also did 4 years in the middle at Aberystwyth. All of which was very pre-SSiW. My natural accent in English is a mix of South Wales, Herefordshire and Forest of Dean which doesn’t help either! ;-). All that means that my Welsh is a bit of a mish-mash - some words still come out with a more Southern pronounciation, and some with a more Northern one.
There is a subtle difference with some words - actually there are some subtle-as-a-brick differences too - and I must admit sometimes I can’t even remember whether I am using a Southern or a Northern variation! For instance, pethau can be peth-eye, peth-er, peth-ah, but I honestly can’t tell you which belongs in which part of Wales without looking it up!
The wy sound, particularly because it is a combination of vowels, does get pronounced differently. For example, you’ll hear the name Myfanwy said (sung!) with an oi sound at the end or a we sound at the end. However, debygrwydd is, I’m pretty sure, always the oi sound, but in gwyddfid (honeysuckle) the wy is a ‘wi’ (as in with).
Now might be a good time to say that although I started and named this thread, I wouldn’t say I have all the answers - just thought it would be a handy single place to collect tips and exercises for awkward sounds - so everyone’s input is very welcome! 
As that just happens to be my name…
I say it with a very slight emphasis on the “oo” sound as it slides into the “ee,” but not a flat “weee.” Another Myfanwy I know says it without any “ee” sound at all, just the “oo.”
The only thing that really bothers me is when people call me “Muh-FFAWN-ee” (“ffawn” as in “a baby deer”). Americans are notoriously bad with names in other languages. You ought to hear us trying to pronounce the athletes’ names during the Olympics!
Just for curiousity’s sake: is there a peculiarly Gog or De or Gorllewin way to pronounce Myfanwy?
The one I always end up saying to people is the CH sound.
I find that everyone I speak to can be sorted out by doing this.
Write down “The Loch Ness Monster”
Get them to say it out loud.
99% of people get it right.
Tell them that the closing sound in “Loch” is identical to our CH.
Write down “Johann Bach” (The piano guy!)
Get them to say it out loud.
99% of people get it right.
Tell them that the closing sound in Bach is identical to our CH!
Why?
Because Bach is our word!
Spend the next half hour trying to convince them that Johann Bach was named so because he was so small.
Yes! I was trying to think of a way to describe the difference, and tapped vs trilled is exactly it.
Trilled: rrrrrrrrrr
Tapped: say “uhr… uhr… uhr,” with just a single tap of the tip of your tongue on the roof of your mouth behind your teeth (what Catrin describes as the alveolar ridge. You’ll feel it if you poke around a bit).
If it comes out voiced as “uhr-uh… uhr-uh… uhr-uh,” it’s plenty close enough; in fact, that would be a good start. You’ll learn to cut the extra “uh” off later as the sound and the sensation of tapping the R become more familiar.
Catrin often taps her Rs, especially in words like trio and drio, and I would imagine that a tapped R in place of a trilled one wouldn’t raise a single eyebrow. I think the point is for it not to be a “cupped” R as is usual in English, and which sounds very different.
@siaronjames I don’t think I’ve come across any other phrases with “yn ôl” in them yet. I can do the “wyth” part of “wythnos yn ôl” but the “nos yn ôl” part gets my tongue in a knot. It’s not helped by not being totally sure what sounds I’m hearing when “wythnos yn ôl” comes up in the lessons.
I’m doing the Southern version.
Phonetically in English noss-uh-nawl, if that helps.