Comparing the podcasts produced by NotebookLM and Lettercast.ai using the same single sources (pdf or text)

Sources	NotebookLM	Lettercast.ai	NotebookLM greater by
Iconic British Designs: The London Tube Map and the London Eye	218 seconds	153 seconds	42%
	https://notebooklm.google.com/notebook/7e91a45e-e544-4447-98b3-e19889f99463	https://app.lettercast.ai/casts/0f2bd232-b44a-4983-af32-f6f4e559c66d.mp3
	647 words	375 words	72%
	178 wpm	147 wpm	21%
	GSE level: 62 - 66	GSE level: 58 - 62	7%
	CEFR level: B2	CEFR level: B2	=
Social rules in my country	314 seconds	129 seconds	143%
	https://notebooklm.google.com/notebook/d6ec3dd2-cb55-4087-b228-20e0b6de8525	https://app.lettercast.ai/casts/b5fae50f-80f1-4376-97ea-bb515483db56.mp3
	947 words	310 words	205%
	180 wpm	144 wpm	25%
	GSE level: 64 - 68	GSE level: 55 - 59	16%
	CEFR level: B2	CEFR level: B1+	+
Eat and drink – at the right time!	252 seconds	172 seconds	47%
	https://notebooklm.google.com/notebook/af091734-070b-464c-b5b5-64617d0a355c	https://app.lettercast.ai/casts/450f171b-b2fe-4d85-8c6c-e1e4fa3e57f4.mp3
	797 words	405 words
	190 wpm	141 wpm	97%
	GSE level: 62 - 66	GSE level: 62 - 66	35%
	CEFR level: B2	CEFR level: B2	=
Spanish honeymoon couple on the Titanic	267 seconds	126 seconds	112%
	https://notebooklm.google.com/notebook/39bc7cb2-54e4-407e-a6cd-24c031f7350c	https://app.lettercast.ai/casts/7f3bf733-92c1-46d3-9773-c9276b5940c1.mp3
	823 words	309 words	166%
	185 wpm	147 wpm	26%
	GSE level: 57 - 61	GSE level: 62 - 66	-8%
	CEFR level: B2	CEFR level: B2	=
Averages	263 seconds	145 seconds	81%
	804 words	350 words	130%
	183 words per minute	145 words per minute	26%
	GSE level 63	GSE level 61	3%
	CEFR level B2	CEFR level B2	=

 

There are some major differences between these two ways of generating podcasts. NotebookLM is much faster and the interface is much more sophisticated and it’s much easier to share the recordings. What’s more Lettercast only accepts PDF files as sources. NotebookLM even lets you upload audio files now!

The podcasts produced by NotebookLM are 81% longer on average and 26% faster, which means that the number of words is more than double (130% more). The levels on the GSE and CEFR scales are very similar (B2) and suitable for students at B1 and up, but not lower.

The major problem  with the NotebookLM podcasts is that they are very fast: 183 words per minute. NotebookLM allows you to play them at 80% which means the speed would be about 146 wpm, much the same as Lettercast. Sadly, Lettercast only allows you to play the podcast faster!

My suggestion is to use Turboscribe.ai to get a transcript of the podcasts which can then be listened to with the script highlighted section by section, although you have to move the page up all the time.

From NotebookLM you can download the .wav file and then upload it to Turboscribe, specify that there are two speakers and click on TRANSCRIBE. You can change the speed to 75%, which will reduce the speed to about 137 words per minute.

From Lettercast.ai It is more complicated. You need to click on View all and then on the orange RSS feed icon, find the link to the audio file which is an .mp3 file select it and select Copy and paste the link into Turboscribe, specify that there are two speakers and click on TRANSCRIBE. 

A further problem with Lettercast.ai is that now I have made 5 podcasts, I don’t seem to be able to make any more on my free account although it specifies 20 free podcasts per month.