Fixed point toolbox and fft

hi,
      I have written program for fft in M file and using fixed point
toolbox i simulated FFT . The final results` WordLength was 35 and
FractionLength 27. I then took normal fft and compared results ,error was
in the range of 10^-3. 

      Just for curiosity i converted output of  normal(Double Precision )
fft
into fixed point using fi. The resulting fi object was having WordLength
of 16 and FractionLength of 12. And error almost zero. Now how is this
possible , a higher FractionLength should have shown less error isnt it?

On Aug 3, 12:56 am, "sudarshan_onkar" <sudarshan.on...@gmail.com>
wrote:
> hi,
>       I have written program for fft in M file and using fixed point
> toolbox i simulated FFT . The final results` WordLength was 35 and
> FractionLength 27. I then took normal fft and compared results ,error was
> in the range of 10^-3.
>
>       Just for curiosity i converted output of  normal(Double Precision )
> fft
> into fixed point using fi. The resulting fi object was having WordLength
> of 16 and FractionLength of 12. And error almost zero. Now how is this
> possible , a higher FractionLength should have shown less error isnt it?

Normalization issue?  That would be my guess.

Julius

>On Aug 3, 12:56 am, "sudarshan_onkar" <sudarshan.on...@gmail.com>
>wrote:
>> hi,
>>       I have written program for fft in M file and using fixed point
>> toolbox i simulated FFT . The final results` WordLength was 35 and
>> FractionLength 27. I then took normal fft and compared results ,error
was
>> in the range of 10^-3.
>>
>>       Just for curiosity i converted output of  normal(Double Precision
)
>> fft
>> into fixed point using fi. The resulting fi object was having
WordLength
>> of 16 and FractionLength of 12. And error almost zero. Now how is this
>> possible , a higher FractionLength should have shown less error isnt
it?
>
>Normalization issue?  That would be my guess.
>
>Julius
>
>

You mean to say Scaling is not proper?