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Entries in Dave Immer (8)


In Or Outside The Box: Is it the Codec or the Network? by Dave Immer

I have noticed in some blogs a tendency to intermingle codec problems with network quirks.

For instance, Source-Connect is an excellent piece of software that delivers very good audio using the AAC algorithm. When the network over which it is running is up to the task, results are satisfying. But a user expecting to get an “ISDN experience” from it when their internet service is experiencing packet collisions, jitter and bursty or slow performance, may have a tendency to associate such behavior with the software codec itself when that is not the case.

Another example would be the Telos Zephyr. Being as the Zephyr is immensely popular and has emerged as the standard ISDN codec (in the US,) people tend to co-mingle it’s behavior in their minds with the ISDN line to which it is connected. While the Zephyr is a well designed, user friendly box, it can be unstable compared to other major brands. The characteristics of such a “standard” codec might be perceived as the nature of ISDN itself, which, again, is not necessarily so.

Certainly troubleshooting is inevitable with any unit. And unless you have the option of substituting alternate equipment, networks or software, it’s way harder to arrive at a clear understanding of the problem(s.) So:
1. Rent one or ask a colleague if you can borrow their codec and try it on your line.
2. Take your codec over to a colleague’s network and try it on their line.
3. Involve a third party like the Digifon Bridge to make test connections. 
This way you can at least determine if the issue is in or outside the box (or both!)

Let me know if you have comments about this.                   Thanks,

Dave                             Complete library of newsletters:


IP Codecs: Main or Backup/Alternate? by Dave Immer

If an IP codec is your main live audio networking tool, then it’s probably because
A. You can’t get ISDN or are unwilling to pay for it,
B. Most of your clients use IP anyway.
But if ISDN is your primary codec, you should definitely also have an IP codec. This gives you security as a backup, plus flexibility to connect with compatible IP-only systems. And everybody can get IP.

With ISDN MPEG codecs from companies such as Telos, Musicam, APT, Mayah, Prodys, TieLine, AudioTX, etc, compatibility is not (usually) an issue, as manufacturers long ago agreed on connection standards. But with IP codecs, it’s still kind of like the wild west with Source-Connect on it’s proprietary (albeit popular) mountain, and most other IP codec companies providing limited cross-compatibility despite employing standard algorithms such as AAC and MPEG layers II & III.

No matter what IP codec you use, the usual internet problems will persist such as latency and uncertain reliability. But these disadvantages can be minimized with the right algorithms on the right hardware platform over the right network. My recommendation for IP codecs:

1. Algorithm: APTX or AAC Low Delay
2. Hardware Platform: Musicam Suprima family or Source-Connect on a fast Intel-based processor.
3. Network: 15Mb/5Mb cable/fios/u-verse

Let me know if you have another IP codec you particularly like.                    Thanks,

Dave                             Complete library of newsletters:


WAKE UP! (Your ISDN Codec, That Is...) by Dave Immer

Both you and the remote facility are configured identical, the calls connect, but only one side is locked (framed). But when audio signal gets sent to the un-locked end, it becomes locked. If you own an older ISDN codec model such as the Telos Zephyr (both Classic & Xstream) or the Musicam Prima (both CDQ & LT) you may, from time to time, need to receive audio to ‘wake up the box.’

Of course, the user that needs to send the audio signal to wake up the other end doesn’t know the other end is not locked, since the locked (framed) condition only pertains to the decoder (receive.) So it’s good to send some signal as soon as the dial-up connection is made to make sure the remote side codec is ‘awake.’

I have also seen phantom signal appear on codec meters looking like a steady noise level, only to go away once an ISDN connection is established.

Often the equivalent of jiggling the wires or toggling the switch clears up the issue.

Sometimes a reboot is needed to get stuff to work. (The display on the Zephyr may show ‘Ready/Ready’ but the box cannot make or receive calls.) I put this in the same category as wire jiggling since no settings get changed to remedy the condition.

Let me know if you have questions about waking up the box.                  Thanks,

-Dave                     Complete library of newsletters:


Loop-back Connections - Essential Tests for ISDN and Source-Connect by Dave Immer


Being able to confirm your codec system is operating properly or to identify the source of a problem is a basic procedure we should all have in our back pockets.  A network loop-back test can accomplish this easily and provide valuable insight:

1.) It shows you that your signal path is set up correctly. You should hear the signal that you are feeding to the codec input “slap back” to your codec output.
2.) It confirms your network is passing the bit-stream in both directions.
3.) For ISDN users it confirms your long distance carrier is cooperating.
4.) For Source-Connect  it confirms your bit-rate and receive buffer are set at usable values.

Source-Connect users can connect to one of the “echo” sites on the contacts list.

ISDN users can dial an AT&T ISDN number set up for this purpose: 732-758-9999. This number can be dialed multiple times depending on your codec bit-rate. For instance if your codec is in L2Mono128 mode you would make 2 calls to this same number. If you need to test an APTX codec at 384kbs you would make 6 calls. If the calls don’t go through (meaning you either have no long distance carrier or your long distance carrier is failing to complete the calls) try dialing from one line to another. These would be local calls.

Doing this test prior to your first session of the day is a quick, easy way to confirm all is well.

Let me know if you have questions about loop-back test connections.   Thanks,

-Dave                                Complete library of newsletters:


Can You Sling the ISDN/IP Lingo? by Dave Immer

Some acronyms and contractions have embedded themselves in our daily discussions of configuring, using and troubleshooting our live audio networks.

Here are some common ones in no particular order:

PSTN: Public Switched Telephone Network
ISDN: Integrated Services Digital Network
SPID: Service Profile IDentifier
CODEC: COder/DECoder
Telco: Telephone Company
TA: Terminal Adapter
IMUX: Inverse Multiplexer
kbps or kbs: Kilobits Per Second
BERT: Bit-Error Rate Test
LEC: Local Exchange Carrier
CIC: Carrier Identification Code
PIC: Primary Interexchange Carrier
CPE: Customer Premise Equipment
IP: Internet Protocol
QoS: Quality of Service
FEC: Forward Error Correction
SIP: Session Initiation Protocol

Let me know if there are other ones you encounter often.   Thanks,

-Dave                              Complete library of newsletters: