Yes, the ch can sound quite like an /h/ in some dialects, and with this lady I can hardly hear any difference between the cha and the tha in the sentences on this page.
So best to concentrate on the bits that are distinctive. In chan eil the first syllable is not stressed but the second and there is a distinct n. D
Scottish Gaelic, as far as I know, doesn’t have a voiced–voiceless contrast in stops, it rather have lenis stops (unaspirated and voiceless) and fortis ones (aspirated and also voiceless).
The stops transcribed using the characters in Latin used for voiceless stops: p, t, c are fortis – aspirated: [pʰ, t̪ʰ, kʰ] (just like English p, t, k – English aspirates them too – except that Gaelic t is dental), and they get pre-aspirated to [xp, xt̪, xk] or [ʰp, ʰt̪, ʰk] after vowel in first syllable: mac [maxk] (as if it were
The ones written down using characters traditionally used for voiced stops: b, d, g are lenis – they are also voiceless but unaspirated: [p, t̪, k], sometimes transcribed as [b̥, d̥, ɡ̥] – but that means the same, voiceless [b̥] is just [p]. In that they differ from English b, d, g, as the English ones are both voiced and unaspirated. They do get voiced after nasals though: bàta a boat is [paːʰt̪ə] but am bàta the boat is [əm baːʰt̪ə], or get fully nasalized: [ə maːʰt̪ə], depending on the dialect.
At least that’s what Wikipedia and Akerbeltz in the Voiced vs Voiceless or Why does b sound like p but not really? article have to say about them. In the latter:
And Gaelic works just like Cantonese in this respect. Gaelic b, p, d, t, g, c are all voiceless, both broad and slender. So which one is which? b, d, g are simply voiceless, p t c are voiceless and aspirated at the start of a word, so in a pair like gas vs cas, the only difference between the two will be a puff of air following c.
Now, since English also has the distinction of aspiration, English ear can hear the difference between Gaelic b and p as they do differ by one of the features they also differ in English. And Gaelic speakers are accustomed to hearing English, so I believe that if some one uses English [pʰ] and [b] (instead of [pʰ] and [p]), native speakers still perceive that as good Gaelic.
That’s also different from Irish, where they do have voiced stops (while the voiceless ones are aspirated – like in English and Gaelic, but they don’t have preaspiration).
So in Irish Albain Scotland is pronounced [ɑɫ̪əbˠənʲ] while in Sc. Gaelic Alba is [aɫ̪apə]. And cat a cat is [kʰɑt̪ˠ] similar to Sc. Gaelic cat [kʰaʰt̪] (only without the preaspiration before t).
Now, after the s and ch only voiceless stops occur, but they are also unaspirated – so they sound neither really like p, t, c (those should be aspirated), nor like b, d, g (those should be voiced). Hence in older Irish literature variation in spelling of such words as scéal vs sgéal, bocht vs bochd, Gaedhealtacht vs Gaedhealtachd, taispeáin vs taisbeáin, etc. In modern spelling it’s been settled that the voicedness is a more important feature and today Irish writes always scéal, bocht, Gaeltacht, taispeáin.
But in Scottish Gaelic there is no voicedness contrast and thus, since the stops after s and ch are unaspirated, they are rather written as b, d, g: sgeul, bochd, Gàidhealtachd, taisbean.
For some reason, though (I guess traditional aesthetics won), both languages write sp in the beginning of words: spíosrach and spìosrach, spealadóir and spealadair, even though in Gaelic the words sounds more like
First, to be very technical, we are privileged on this course (compared to many other Duolingo courses) to have a sample of real speakers. They (the course preparers and the recording artists) have spent a lot of their own time doing this for us. This means we are bound to have outliers unless the distribution is truncated (which translates as censoring people).
I have listened to all the sentences with glic in. They all sound to me like they are recorded by the same woman. Whilst technically several of her phonemes are outliers, this is because they are canonical. That means they are extremes of the distinctive Gaelic sounds that you have to get used to. So I would say this is really useful pronunciation. If you get used to this, you will find it really easy to understand the vast majority of Gaelic accents.
I would not say this applies to all the sentences in this course. Some of them are not so much canonical as downright unusual. These I do not consider helpful to a learner.