Input Latency

A second issue of latency, unrelated to monitoring latency, is the latency that occurs in a card's inability to process and digitize audio in, shall we say, a timely manner. This will result in the actual recorded audio being a sample or two (possibly more) later than the incoming audio. This issue will compound itself if the next recorded track is created while referencing to the first track. In other words, the first track will be 'x' number of samples late, and the second track will be x + x samples late.

You won't often hear the question, "What's the input latency?" The question more often asked is, "Is the card frame accurate?" I don't know why this is. Maybe it seems more of a critical issue when synchronization is involved, where digitized audio is immediately referenced to a source. This issue spills over to any type of capture card, so it's even possible that it originated in video capture while locking to timecode, more the norm when capturing video. However you splice it, this is another important latency issue. There are in fact audio cards on the market that have zero input latency. Again, check with the manufacturer.

Windows Latency

The third version of the latency issue involves a device that uses Windows drivers, also referred to as MME (multi-media extensions). Windows latency can be as high as 50 or 75 milliseconds, so that 'tape type' monitoring is not feasible using only MME drivers. Waiting 50 or 75 ms is a heck of a lot of time to hear the monitoring signal of something you've just played. That's similar to the timing you'd use in a slapback delay.

A program like Steinberg's Cubase will have an ASIO MME emulation mode, as well as ASIO DirectX. These would be the logical choices if using an ASIO compliant program and an audio card that does not provide ASIO drivers. If your sound card utilizes DirectX drivers, ASIO DirectX would be your first choice over ASIO MME.

Latency with DirectX

DirectX is part of the Windows operating system, and basically gives programmers faster communication between the application and the hardware. This is the same attempt that ASIO makes, only its less effective. DirectX is constantly updated, and there are certainly newer versions than the one that came with Win95 or 98. For the record, there are different components of DirectX for video and audio, and "Direct Sound" is the audio portion of DirectX. Many software synths on the PC side use DirectX, so it is essential that your audio device driver be DirectX compliant. Audio latency when playing software synthesizers is a side issue, but involves the "L" word nonetheless.

Getting Around the Latency Issue, Mac & PC

The way that the digital recordist can get around the issues of latency while monitoring is to monitor the hardware inputs of the audio card. Pre-ASIO, this was common practice. Most sound cards have a control panel that would allow you to select the hardware input as your monitoring source, or designate at which output you wish to monitor the input signal. Other sound cards will use the Windows mixer, accessed by double clicking the speaker icon on the taskbar or by going to Control Panel | Multimedia | Audio Properties or some variation thereof in Windows 2000). In the Mac OS, Control Panel | Sounds will allow you to monitor the inputs by simply checking a checkbox.

In the Mac though, ASIO is almost a necessity since Sound Manager limits you to only one stereo pair for both input and output (though the input and output pair may be individually selectable). Most audio programs on the Mac these days use ASIO or a similar format, though most likely a proprietary one (such as Emagic's EASI or Motu's MAS). One stereo pair is often fine for editing, but you didn't buy a multi-port sound card to be limited to one stereo pair. Windows itself is limited to one stereo pair, but the programs that use MME override the Windows settings and enable multiple stereo ports.

By monitoring the hardware inputs while recording, one can quite effectively use a program that utilizes Windows MME, such as Cakewalk. Even Steinberg has created a way to get around the ASIO latency with their "Direct Monitoring" option (ASIO 2 only) in their Audio Setup page, but some sound cards limit its functionality.

Ultimately, finding a way for programs to monitor the hardware inputs that disables them while in play mode and enables them in record mode will be the most effective means by which we perform hard disk recording. Latency is not really an acceptable commodity, in my opinion, if we're talking about a pro audio format. The solution may lie in a direct communication between the software and the sound card via the sound card's control panel.

JD Mars is the producer of DigitalProSound. He has extensive experience in the professional audio business, including stints as the Chief Engineer at Duplex Sound in NYC and in technical support at Midiman/M Audio.