[Dtb-talk] Converting tone indexed books to DAISY

[Tim Valley]

Greg,

I originally used a software FFT (Fast-Fourier Transform) routine preceded
by a software low-pass filter to detect tones (for the Minnesota State
Services f/t Blind Digitization Project).

The results were mixed (and slow), so I implemented a much simpler and
significantly faster approach:  I simply count the number of cycles in a
given buffer size.  If you know the size of the buffer as it relates to the
sample rate, you can directly relate this count to frequency.  I still use a
low-pass filter to remove everything above about 120 Hz (at 2x speed, or 60
Hz for real-time speed).  The low-pass filter thus helps to remove any
"distractions" that would otherwise need to be ignored.

It also helps to do an RMS Normalization step between the LPF and the
counter, or even before the LPF so that the tones appear at a significantly
higher level than the residual noise, wow and flutter.  When counting
cycles, you have to use a threshold level that is offset from the
zero-crossing point so that you aren't counting the low-level dither, noise,
wow and flutter as they each cross zero.

The module that I created can distinguish between 25 Hz and 35/50 Hz tones
(just different counts) in order to separate PAGE tones from CHAPTER tones.

Unfortunately, my code is in Borland's Delphi (a visual PASCAL), so I doubt
you'd find it very useful.  Let me know if you're interested in more
details.

  
Tim Valley
MacroMedia, Inc.
MN State Services f/t Blind
SSB 21st Century Plan
Project Coordinator
Tim at mmAirForce.com
952-432-2774


-----Original Message-----
From: dtb-talk-bounces at nfbnet.org [mailto:dtb-talk-bounces at nfbnet.org] On
Behalf Of Greg Kearney
Sent: Thursday, December 28, 2006 2:04 PM
To: Discussion of Digital Talking Books
Subject: Re: [Dtb-talk] Converting tone indexed books to DAISY

When I first started this I tried recording the fast forward speed. It  
was too fast and resulted in poor quality recording I think 4X would  
be as fast as I would ever care to go.

The problem with detecting the index tone is that it is placed over  
the top of the recording. So it does not stand alone in the recording  
as a tone but rather is mixed in with the normal narration. It is easy  
to see on the display but would be hard to detect with a program as  
each tone would be mixed in with different narration.

Greg Kearney
On Dec 28, 2006, at 12:53 , Brett Winches wrote:

> I have a telex 6120 which will do 15 x but it also has inbuilt  
> processes
> to do on the fly conversions so that the original audio quality is
> maintained.  This unit has a interface to let you drop files with  
> index
> marks on them from hd to cassette and vis versa but I do not have this
> software.  As this unit is no longer actively supported by TELEX I do
> not intend to acquire the software for this purpose.  I have a working
> relationship with our library for such conversion needs.
>
> BTW I do have the NLS standards for tone indexing around here  
> somewhere,
> (frequency, time duration, interval between tones etc.) but it also  
> may
> be available on their website somewhere.
>
>
> Regardless this is a good trick.  Writing a subroutine to automate the
> marking process should not be hard, but I do not know if studio  
> recorder
> code is available.
>
>
> BRETT WINCHESTER
> bwinches at icbvi.idaho.gov
> -----Original Message-----
> From: dtb-talk-bounces at nfbnet.org [mailto:dtb-talk-bounces at nfbnet.org]
> On Behalf Of Irwin Hott
> Sent: Thursday, December 28, 2006 12:23 PM
> To: Discussion of Digital Talking Books
> Subject: Re: [Dtb-talk] Converting tone indexed books to DAISY
>
> There are cassette decks that will play at 3 & 3/4 IPS, but I would
> suspect that the loss in quality at recording 4 times the normal speed
> would be significant.
>
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