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Help making PCM file ?

Jul 5, 2010 11:07 AM

I need to make a file that must have:


Format: PCM

Bit Rate: 8 Bit

Channels: 1(Mono)

Channels: 8kHz

Sample Size: 8 Bit A-low compressed


I use Adobe Audition 3.0

The problem is that after exporting the way i think it should be done, the track sounds distorted and slow. Please tell step by step how to make it succesfully and fast.


Thank You!

  • Currently Being Moderated
    Jul 6, 2010 1:25 AM   in reply to marybib

    It would be interesting if someone else could try this, as I thought I'd just see what happened here. I haven't used this sort of encoding for at least 15 years and can't remember much about it.


    I have tried with both Audition 3 and 1.5 on different machines. Taking the file down to 8-bit, 8kHz, mono makes it sound noisy and bandwidth limited as expected. Then encoding by saving using the mu-law option doesn't seem to make much difference to the sound but, although it is reported as encoded, the file length seems to remain the same as the uncompressed file.


    Choosing the A-law option results in a file that, when re-loaded is over 40dB down and, when amplified, sounds very distorted and noisy.The file size still reports as the same, though.


    The whole thing makes me think I must be doing something stupid, but I can't see what. I don't get any speed changes, though.

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    Jul 6, 2010 2:41 AM   in reply to Wild_Duck

    Just followed your work flow with exactly the same results.


    I can't work out what's happening either.

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  • Currently Being Moderated
    Jul 6, 2010 7:07 AM   in reply to Bob Howes

    I think I have worked out what to do....


    1. Record file in standard wave format

    2 Convert sample type to 8kHz, mono, 16-bit

    3. Save as a-law (checking the a rather than mu option). This automatically converts the 16-bit to 8-bit.


    The quality is, as expected, pretty awful.


    There appears to be a sort of tiny bug here in that no warning is given when the Save function is sent the wrong format. It has worked this way since Cool Edit 1.53 (I've just tried), but the 1.53 help files gave the vital clue about the 16 to 8 bit conversion. I can find no mention of this in the AA3 help files.


    It would be useful to know if this solves all the OP's problems.

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  • SteveG(AudioMasters)
    5,602 posts
    Oct 26, 2006
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    Jul 7, 2010 1:56 AM   in reply to marybib

    marybib wrote:


    I'm not sure if i understand u correctly. Maybe now i will make situation more clear: Cell phone company gives me songs in mp3 format usually and my goal is to convert them to:     format PCM

                                               bit rate 8 Bit

                                               channels 8kHz


                                               sample size 8 Bit A-low compressed

                           (i don't see a 8kHz option anywhere, it start from 8000)



    I think you're a bit confused, and the detail may be important. A bit rate is expressed in ksamples/sec. Channels are the number of them available - generally either one or two (mono or stereo). The sample size is the total number of samples in your file (generally irrelevant). What I think you mean is that the bit depth is 8-bit, the sample rate may be 8ksamples/sec, and 8k = 8000 anyway, so what's the problem? The file format is A-law, not A-low - that doesn't exist. Everything else you need you've been told.

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  • Currently Being Moderated
    Jul 7, 2010 2:57 AM   in reply to SteveG(AudioMasters)

    There are several things here that can and will cause confusion, so the first thing should be to sort out what to achieve and how you plan to work. It seems to me that you have to work from.....


    1. An mp3 compressed input file of unknown format. Load this into Audition 3  This converts it as it loads to a temporary pcm file of the same original underlying format within Audition because Audition internally works with uncompressed pcm files.

    This file now needs to be converted inside Audition to be ready to save in the output format you are aiming for.


    2. Go to Edit-> Convert Sample Type and select Sample Rate 8000 Hz     Channels Mono     Bit Depth 16 bit.    You can save this as a preset in that screen if you like. OK and close Convert sample type screen.


    3.Hit File-> Save As and select A/mu Law Wave, hit the Options button at the bottom of the screen and select A-Law 8-bit on the pop up window.


    Here, I suggest you save to a specific output directory and/or with a carefully selected file name as the files will be in this peculiar compressed-for-telephone format and you don't want them mixed in with 'normal' uncompressed wave files. Hit the Save button cross your fingers and hope.


    For the first 2 or 3 times, I suggest you save the file, close Audition and check you can re-load and play the file. This ensures you have actually produced a working file.


    Edit: The one thing that is still a bit vague here is that if you do reload the final A-law file and go to File->File Info, it is shown as an ACM Waveform A-Law format. I think this is probably OK.

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