There are a lot of German dictionaries online with audio facility where you can hear the sound.
The ch-sound after the vowel a is different from the ch-sound after i.
I simply call the first ch "Bach-sound. When you pronounce the German word Bach the mouth opening is wide for the vowel a. When you pronounce the ch-sound
you keep this wide mouth opening and the air stream from your lungs passes the vocal cords, which have the widest opening, without any vibration.
The sound of this German ch might be compared to the rough sound of an angry cat.
When you pronounce the ch-sound after the vowel i as in the word ich, your tongue position in the mouth room is high when you pronounce i.
The ch-sound after i, which I simply call ich-sound is produced exactly in the same way as the Bach-sound, only with small mouth opening as it is necessary for the vowel i.
The two different ch-sounds have two different phonetic signs. Actually this wouldn't be necessary.It is almost impossible to produce a Bach-sound after i
or an ich-sound after a. You would have to speak two separate syllables and you would have to change the mouth opening.
I don't know whether this theoretical explanation will help you. Normally a teacher produces the sounds, explains to you how these sounds are produced,
and corrects you when you don't hit it with the first go.
I'm and old man and my knowledge of technical things in the computer sector are limited. Otherwise I would like to make a video about the way of producing
I have just had a look at a youtube video "German "CH" Pronunciation". The speaker talks a lot, but I don't think that that way will teach someone how to pronounce German ch. There are several things to show: The mouth cavity, the mouth opening and the tongue position when you pronounce the vowels /a/ and /i/. This can best be shown by diagrams showing the mouth room in a vertical cut so that one sees the mouth cavity and the tongue position from the side. When producing an /i/ the lip position changes. This can be shown with diagrams showing the mouth from the front.
The second important thing is a the behaviour of the vocal cords. There are models that can give an understanding of the vocal corrds, but it is important to convey a feeling for the vocal cords. When someone produces the loud sound of a long /aaaaa/ the vocal cords are opened wide and without any tension. They begin to vibrate and one can feel this vibration in the throat clearly. When someone produces the sound /h/ a light air stream from the lungs passes through the vocal cords without any vibration. When we produce a strong air stream the vocal cords get tension and the typical ch-sound is produced. The vocal cords are open and tense, there is no vibration. As I said before it is the sound of an angry cat.
This can't be shown with diagrams . The learner has to produce the different sounds and observe what things happen during articulation.