Downsampling and applying a lowpass filter to digital audio

Posted by twk on Stack Overflow See other posts from Stack Overflow or by twk
Published on 2008-10-26T18:12:07Z Indexed on 2010/03/26 17:23 UTC
Read the original article Hit count: 423

Filed under:

downsampling

|

dsp

|

pcm

|

audio

I've got a 44Khz audio stream from a CD, represented as an array of 16 bit PCM samples. I'd like to cut it down to an 11KHz stream. How do I do that? From my days of engineering class many years ago, I know that the stream won't be able to describe anything over 5500Hz accurately anymore, so I assume I want to cut everything above that out too. Any ideas? Thanks.

Update: There is some code on this page that converts from 48KHz to 8KHz using a simple algorithm and a coefficient array that looks like { 1, 4, 12, 12, 4, 1 }. I think that is what I need, but I need it for a factor of 4x rather than 6x. Any idea how those constants are calculated? Also, I end up converting the 16 byte samples to floats anyway, so I can do the downsampling with floats rather than shorts, if that helps the quality at all.

© Stack Overflow or respective owner

Related posts about downsampling

Reducing moire when downsampling halftone comic images.

as seen on Stack Overflow - Search for 'Stack Overflow'
How can I reduce moire effects when downsampling halftone comic book images during live zoom on an iPhone or iPad? I am writing a comic book viewer. It would be nice to provide higher resolution images and allow the user to zoom in while reading the comic book. However, my client is averse to moire… >>> More
Downsampling and applying a lowpass filter to digital audio

as seen on Stack Overflow - Search for 'Stack Overflow'
I've got a 44Khz audio stream from a CD, represented as an array of 16 bit PCM samples. I'd like to cut it down to an 11KHz stream. How do I do that? From my days of engineering class many years ago, I know that the stream won't be able to describe anything over 5500Hz accurately anymore, so I… >>> More
Downsampling the number of entries in a list (without interpolation)

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a Python list with a number of entries, which I need to downsample using either: A maximum number of rows. For example, limiting a list of 1234 entries to 1000. A proportion of the original rows. For example, making the list 1/3 its original length. (I need to be able to do both ways, but… >>> More
mp3 downsampling / compression in java

as seen on Stack Overflow - Search for 'Stack Overflow'
Well, i was looking forward to modify the bit rate of a mp3 file in java. I want to downsample(change its bit rate) the mp3 file from 256/384 kbps to say 64/128 kbps.. (I guess this is the only way one can achieve mp3 compression..or is there any other way.?) I searched for LameOnJ but that website… >>> More
When running Adobe Acrobat's OCR on a PDF document, which downsampling produces a higher quality: 600 dpi or 72 dpi?

as seen on Super User - Search for 'Super User'
I have a large PDF document that consists of scanned pages of a textbook. I want to run Adobe Acrobat 9's text recognition function on it, but I'm presented with this menu when I do. I'm confused by the options in the highlighted menu. What option will produce the highest quality/most readable… >>> More

Related posts about dsp

any good free C DSP library?

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi everybody I am developing an application to process geophysical signals; Right now I have done everything in octave and its digital signal processing toolbox, speed is not bad, however the application specifications say I need to port to the final algorithm to C; I am doing lots of filtering,… >>> More
DSP - How are frequency amplitudes modified using DFT?

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to implement a DFT-based equalizer (not FFT) for the sole purpose of learning. To check if it works I took an audio signal, analyzed it and then resynthesized it again with no modifications made to the frequency spectrum. So far so good. Now I tried to silence some frequency bands, just… >>> More
Embedded Systems using FlowStone DSP Programming Language for Windows

as seen on Code Project - Search for 'Code Project'
Developing Embedded Systems Using FlowStone DSP >>> More
TMS320C64x Quick start reference for porgrammers

as seen on Stack Overflow - Search for 'Stack Overflow'
Hello Is thare any quickstart guide for programmers for writing DSP-accelerated appliations for TMS320C64x? I have a program with custom algorythm (not the fft, or usial filtering) and I want to accelerate it using multi-DSP coprocessor. So, how should I modify source to move computation from main… >>> More
Is Objective C fast enough for DSP/audio programming

as seen on Stack Overflow - Search for 'Stack Overflow'
I've been making some progress with audio programming for iPhone. Now I'm doing some performance tuning, trying to see if I can squeeze more out of this little machine. Running Shark, I see that a significant part of my cpu power (16%) is getting eaten up by objc_msgSend. I understand I can speed… >>> More