Question about 10.4 - "The Sampled Sinusoid" | 2nd Ed FX Book Questions | Forum


Please consider registering

sp_LogInOut Log In sp_Registration Register

Register | Lost password?
Advanced Search

— Forum Scope —

— Match —

— Forum Options —

Minimum search word length is 3 characters - maximum search word length is 84 characters

sp_Feed Topic RSS sp_TopicIcon
Question about 10.4 - "The Sampled Sinusoid"
New Member
January 26, 2021 - 2:54 pm
Member Since: January 26, 2021
Forum Posts: 1
sp_UserOfflineSmall Offline

Hi all, 

I have a question about equation 10.11, page 199 (2nd edition of the FX book)...

In short, the question is: is the equation correct? Smile

It keeps puzzling me, as we are subtracting "M", which is a number of samples, from "nT" which is a value in seconds. I may be entirely missing the point, but it seems to me that equation 10.11 would work if M was a value in seconds, not number of samples. 

In order to delay by a number of samples M, the exponent should be [j * omega * T * (n - M)] rather than [j * omega (nT - M)]. 

I thought this was perhaps a typo or something, but I see that the same equation is used multiple times later on so perhaps I'm just confusing myself...

Does anybody have any thoughts to share? 

Thanks a lot! 


New Member
March 21, 2021 - 6:03 pm
Member Since: March 21, 2021
Forum Posts: 1
sp_UserOfflineSmall Offline

I have this same question.

Have you found a solution yet, Dan?

I've asked my DSP teacher and he says it's probably a mistake in the book, but I would be surprised if it was, since it's used for a long time...

I hope Will could clear this up 🙂

March 22, 2021 - 9:02 am
Member Since: January 29, 2017
Forum Posts: 693
sp_UserOfflineSmall Offline

Hi - yes this is a typo of sorts. It actually has origins in the way I used to teach this, where I took some liberties mixing analog and sampled sinusoid equations. You are correct about it working for seconds rather than samples. I found that students from high-school had no problems with analog sinusoid equations, so I would start there and kind of blend the two together. In the 2nd edition of the book I tried to reconcile that with nT instead of just (t). Sorry for the confusion.


Forum Timezone: America/New_York

Most Users Ever Online: 152

Currently Online:
2 Guest(s)

Currently Browsing this Page:
1 Guest(s)

Top Posters:

Chaes: 56

Skyler: 48

StevieD: 46

Derek: 46

Frodson: 45

Peter: 43

TheSmile: 43

Nickolai: 43

clau_ste: 39

jeanlecode: 37

Member Stats:

Guest Posters: 2

Members: 784

Moderators: 1

Admins: 6

Forum Stats:

Groups: 13

Forums: 42

Topics: 850

Posts: 3372

Moderators: W Pirkle: 693